Fix perl-5.26 @INC path issue at install

Several perl scripts in the config/ directory use modules such as L2hos.pm
and cfgcache.pm, assuming them to be in the current working directory.
Newer versions of perl (since 5.26) fix a security hole introduced by
implicitly searching the current directory for libraries by not
automatcially including the current directory.  Include a fix from newer
versions of latex2html by explicitly including the correct directories
relative to the path of the binary.

diff --git a/config/build.pl b/config/build.pl
index ef2a307..b30fdc1 100755
--- a/config/build.pl
+++ b/config/build.pl
@@ -143,6 +143,9 @@ my ($VERSION) = q$Revision: 1.6 $ =~ /:\s*(\S*)/;
 # --------------------------------------------------------------------------
 
 # Read in the system's configuration
+use FindBin;
+use lib "$FindBin::Bin/..";
+use lib "$FindBin::Bin";
 use cfgcache;
 
 my $dd = $cfg{'dd'};
diff --git a/config/config.pl b/config/config.pl
index 60eb9c4..ad32f52 100755
--- a/config/config.pl
+++ b/config/config.pl
@@ -433,6 +433,9 @@ require 5.00305;
 use Cwd;
 use IO::File;
 use lib 'lib';
+use FindBin;
+use lib "$FindBin::Bin/..";
+use lib "$FindBin::Bin";
 use L2hos;
 
 #use diagnostics;
diff --git a/config/install.pl b/config/install.pl
index 89265de..acf4d20 100755
--- a/config/install.pl
+++ b/config/install.pl
@@ -181,6 +181,9 @@ my ($VERSION) = q$Revision: 1.12 $ =~ /:\s*(\S*)/;
 # Initialize
 # --------------------------------------------------------------------------
 
+use FindBin;
+use lib "$FindBin::Bin/..";
+use lib "$FindBin::Bin";
 use cfgcache;
 use L2hos;