Update regular expressions to work with perl 5.26

Perl 5.26 requires escaping braces in regular expressions.

diff --git a/latex2html.pin b/latex2html.pin
index d670c0d..9981a77 100644
--- a/latex2html.pin
+++ b/latex2html.pin
@@ -1207,7 +1207,7 @@ sub process_ext_file {
 	&slurp_input($file);
 	if ($ext =~ /bbl/) {
 	    # remove the \newcommand{\etalchar}{...} since not needed
-	    s/^\\newcommand{\\etalchar}[^\n\r]*[\n\r]+//s;
+	    s/^\\newcommand\{\\etalchar\}[^\n\r]*[\n\r]+//s;
 	}
 	&pre_process;
 	&substitute_meta_cmds if (%new_command || %new_environment);
@@ -1401,8 +1401,8 @@ sub pre_process {
     &replace_html_special_chars;
     # Remove fake environment which should be invisible to LaTeX2HTML.
     s/\001//m;
-    s/[%]end\s*{latexonly}/\001/gom;
-    s/[%]begin\s*{latexonly}([^\001]*)\001/%/gos;
+    s/[%]end\s*\{latexonly\}/\001/gom;
+    s/[%]begin\s*\{latexonly\}([^\001]*)\001/%/gos;
     s/\001//m;
 
     &preprocess_alltt if defined(&preprocess_alltt);
@@ -1426,13 +1426,13 @@ sub pre_process {
 	&write_mydb("verbatim", $global{'verbatim_counter'}, $3);
 	"$1$comment_mark".$global{'verbatim_counter'}."\n"/mge;
     # Remove the htmlonly-environment
-    s/\\begin\s*{htmlonly}\s*\n?//gom;
-    s/\\end\s*{htmlonly}\s*\n?//gom;
+    s/\\begin\s*\{htmlonly\}\s*\n?//gom;
+    s/\\end\s*\{htmlonly\}\s*\n?//gom;
     # Remove enviroments which should be invisible to LaTeX2HTML.
-    s/\n[^%\n]*\\end\s*{latexonly}\s*\n?/\001/gom;
-    s/((^|\n)[^%\n]*)\\begin\s*{latexonly}([^\001]*)\001/$1/gom;
-    s/\\end\s*{comment}\s*\n?/\001/gom;
-    s/\\begin\s*{comment}([^\001]*)\001//gom;
+    s/\n[^%\n]*\\end\s*\{latexonly\}\s*\n?/\001/gom;
+    s/((^|\n)[^%\n]*)\\begin\s*\{latexonly\}([^\001]*)\001/$1/gom;
+    s/\\end\s*\{comment\}\s*\n?/\001/gom;
+    s/\\begin\s*\{comment\}([^\001]*)\001//gom;
 
     # this used to be earlier, but that can create problems with comments
     &wrap_other_environments if (%other_environments);
@@ -1465,7 +1465,7 @@ sub pre_process {
 	    push(@processedV,$before);
 	    print "'";$before = '';
 	}
- 	if ($after =~ /\s*\\end{$env[*]?}/) { # Must NOT use the s///o option!!!
+ 	if ($after =~ /\s*\\end\{$env[*]?\}/) { # Must NOT use the s///o option!!!
 	    ($contents, $after) = ($`, $');
  	    $contents =~ s/^\n+/\n/s;
 # 	    $contents =~ s/\n+$//s;
@@ -1898,16 +1898,16 @@ sub mark_string {
     # local (*_) = @_; # Modifies $_ in the caller;
     # -> MRO: changed to $_[0] (same effect)
     # MRO: removed deprecated $*, replaced by option /m
-    $_[0] =~ s/(^|[^\\])\\{/$1tex2html_escaped_opening_bracket/gom;
-    $_[0] =~ s/(^|[^\\])\\{/$1tex2html_escaped_opening_bracket/gom; # repeat this
-    $_[0] =~ s/(^|[^\\])\\}/$1tex2html_escaped_closing_bracket/gom;
-    $_[0] =~ s/(^|[^\\])\\}/$1tex2html_escaped_closing_bracket/gom; # repeat this
+    $_[0] =~ s/(^|[^\\])\\\{/$1tex2html_escaped_opening_bracket/gom;
+    $_[0] =~ s/(^|[^\\])\\\{/$1tex2html_escaped_opening_bracket/gom; # repeat this
+    $_[0] =~ s/(^|[^\\])\\\}/$1tex2html_escaped_closing_bracket/gom;
+    $_[0] =~ s/(^|[^\\])\\\}/$1tex2html_escaped_closing_bracket/gom; # repeat this
     my $id = $global{'max_id'};
     my $prev_id = $id;
     # mark all balanced braces
     # MRO: This should in fact mark all of them as the hierarchy is
     # processed inside-out.
-    1 while($_[0] =~ s/{([^{}]*)}/join("",$O,++$id,$C,$1,$O,$id,$C)/geo);
+    1 while($_[0] =~ s/\{([^{}]*)\}/join("",$O,++$id,$C,$1,$O,$id,$C)/geo);
     # What follows seems esoteric...
     my @processedB = ();
     # Take one opening brace at a time
@@ -1922,7 +1922,7 @@ sub mark_string {
         }
         $_[0] = join('',$before,"\{",$after) if($change);
         # MRO: mark one opening brace
-	if($_[0] =~ s/^([^{]*){/push(@processedB,$1);join('',$O,++$id,$C)/eos) {
+	if($_[0] =~ s/^([^{]*)\{/push(@processedB,$1);join('',$O,++$id,$C)/eos) {
 	    $before=''; $after=$';
         }
         if ($after =~ /\}/) { 
@@ -2780,7 +2780,7 @@ sub translate_environments {
 	    $open_tags_R = [ @save_open_tags ];
 	    # check for color
 	    local($color_test) = join(',',@$open_tags_R);
-	    if ($color_test =~ /(color{[^}]*})/g ) {
+	    if ($color_test =~ /(color\{[^}]*\})/g ) {
 		$color_env = $1;
 	    } # else { $color_env = '' }
 
@@ -2791,7 +2791,7 @@ sub translate_environments {
 		$open_tags_R = [ @save_open_tags ];
 		if ($color_env) {
 		    $color_test = join(',',@saved_tags);
-		    if ($color_test =~ /(color{[^}]*})/g ) {
+		    if ($color_test =~ /(color\{[^}]*\})/g ) {
 		        $color_env = $1;
 		    }
 		}
@@ -6507,7 +6507,7 @@ sub parse_keyvalues {
     print "\nATTRIBS: $saved\n" if ($VERBOSITY > 6);
 
     $saved =~ s/$percent_mark/%/g;
-    $saved =~ s/((^|[\s,=])')\\\W{(\w)}/$1$3/g
+    $saved =~ s/((^|[\s,=])')\\\W\{(\w)\}/$1$3/g
 	if $is_german;  #unwanted accents, from active "
     if (@tags) {
 	foreach $tag (@tags) {
@@ -6877,7 +6877,7 @@ sub make_latex{
 	# \usepackage is invalid in LaTeX 2.09 and LaTeX-2e compatibility mode
 	$LATEX_COLOR = ''; $LOAD_LATEX_COLOR = '';
 	# ... so is \providecommand 
-	$preamble =~ s/\\documentstyle[^{]*{[^}]*}\n?/
+	$preamble =~ s/\\documentstyle[^{]*\{[^}]*\}\n?/
 		$&."\n\\let\\providecommand\\newcommand\n"/eo;
     }
 
@@ -7292,7 +7292,7 @@ sub encode_title {
 sub encode {
     local($_) = @_;
     # Remove invocation-specific stuff
-    1 while(s/\\(begin|end)\s*(($O|$OP)\d+($C|$CP))?|{?tex2html_(wrap|nowrap|deferred|)(_\w+)?}?(\2)?//go);
+    1 while(s/\\(begin|end)\s*(($O|$OP)\d+($C|$CP))?|\{?tex2html_(wrap|nowrap|deferred|)(_\w+)?\}?(\2)?//go);
     $_ = &revert_to_raw_tex($_);
     s/\\protect//g;		# remove redundant \protect macros
     #$_ = pack("u*", $_);	# uuencode
diff --git a/versions/html3_2.pl b/versions/html3_2.pl
index 58429ac..0cb404c 100644
--- a/versions/html3_2.pl
+++ b/versions/html3_2.pl
@@ -607,7 +607,7 @@ sub process_tabular {
 
     if ($color_env) {
 	local($color_test) = join(',',@$open_tags_R);
-	if ($color_test =~ /(color{[^}]*})/g ) {
+	if ($color_test =~ /(color\{[^}]*\})/g ) {
 	    $color_env = $1;
 	}
     }
diff --git a/versions/html4_0.pl b/versions/html4_0.pl
index 57c16e2..e77b090 100644
--- a/versions/html4_0.pl
+++ b/versions/html4_0.pl
@@ -955,7 +955,7 @@ sub process_tabular {
 
     if ($color_env) {
 	local($color_test) = join(',',@$open_tags_R);
-	if ($color_test =~ /(color{[^}]*})/g ) {
+	if ($color_test =~ /(color\{[^}]*\})/g ) {
 	    $color_env = $1;
 	}
     }
diff --git a/versions/html4_01.pl b/versions/html4_01.pl
index 9cc3e31..250b5b0 100644
--- a/versions/html4_01.pl
+++ b/versions/html4_01.pl
@@ -976,7 +976,7 @@ sub process_tabular {
 
     if ($color_env) {
 	local($color_test) = join(',',@$open_tags_R);
-	if ($color_test =~ /(color{[^}]*})/g ) {
+	if ($color_test =~ /(color\{[^}]*\})/g ) {
 	    $color_env = $1;
 	}
     }
diff --git a/versions/html4_1.pl b/versions/html4_1.pl
index 9cc3e31..250b5b0 100644
--- a/versions/html4_1.pl
+++ b/versions/html4_1.pl
@@ -976,7 +976,7 @@ sub process_tabular {
 
     if ($color_env) {
 	local($color_test) = join(',',@$open_tags_R);
-	if ($color_test =~ /(color{[^}]*})/g ) {
+	if ($color_test =~ /(color\{[^}]*\})/g ) {
 	    $color_env = $1;
 	}
     }