Add DLZ test for LDAP libraries without paths

When compiling with dlz and ldap support enabled, the configure script will
search /usr/lib before the default library directory.  This can add a
-L/usr/lib to the library flags.  With SYMLINK_LIB=no on multilib
x86_64/x86_32 Gentoo systems, this causes the linker to find and warn about
32-bit libraries.  If any of them are libtool libraries, libtool will
replace the -l flag with exact paths to the 32-bit libraries in a 64-bit
compile, resulting in a failure.

diff --git a/contrib/dlz/config.dlz.in b/contrib/dlz/config.dlz.in
index 0000000..0000000 100644
--- a/contrib/dlz/config.dlz.in
+++ b/contrib/dlz/config.dlz.in
@@ -368,38 +368,82 @@ AC_ARG_WITH(dlz_ldap,
 			       (Required to use LDAP with DLZ)]),
     use_dlz_ldap="$withval", use_dlz_ldap="no")
 
-if test "$use_dlz_ldap" = "yes"
-then
-	# User did not specify a path - guess it
-	ldapdirs="/usr /usr/local /usr/pkg"
-	for d in $ldapdirs
-	do
-		if test -f $d/include/ldap.h
-		then
-			use_dlz_ldap=$d
-			break
-		fi
-	done
-fi
-
-if test "$use_dlz_ldap" = "yes"
-then
-	AC_MSG_RESULT(not found)
-	AC_MSG_ERROR(
-[LDAP headers were not found in any of $ldapdirs; use --with-dlz-ldap=/path])
-fi
-
 case "$use_dlz_ldap" in
 	no)
 		AC_MSG_RESULT(no)
 		;;
 	*)
-		DLZ_ADD_DRIVER(LDAP, dlz_ldap_driver,
-				[-I$use_dlz_ldap/include],
-				[-L$use_dlz_ldap/lib -lldap -llber])
+		if test "yes" = "$use_dlz_ldap"
+		then
+			# User did not specify a path - guess directories
+			ldapdirs="/usr /usr/local /usr/pkg"
+		elif test -d "$use_dlz_ldap"
+		then
+			# User specified directory and it exists
+			ldapdirs="$use_dlz_ldap"
+		else
+			AC_MSG_RESULT(not found)
+			AC_MSG_ERROR([path $use_dlz_ldap does not exist])
+			ldapdirs=""
+		fi
 
-		AC_MSG_RESULT(
-[using LDAP from $use_dlz_ldap/lib and $use_dlz_ldap/include])
+		# Search for correct path.
+		# Set both to yes, so we can check them later
+		dlz_ldap_inc="yes"
+		dlz_ldap_libs="yes"
+
+		# See if the compiler can find the library without any paths.
+		AC_MSG_RESULT()
+		AC_CHECK_LIB(ldap, ldap_initialize, dlz_ldap_libs="-lldap")
+
+		for d in $ldapdirs
+		do
+			# Skip nonexistant directories
+			if test ! -d "$dd"
+			then
+				continue
+			fi
+
+			if test -f $d/include/ldap.h
+			then
+				dlz_ldap_inc="-I$d/include"
+			else
+				# Do not search for a library if there is no include.
+				continue
+			fi
+
+			# If a library has been found, search no more.
+			if test "yes" != "$dlz_ldap_libs"
+			then
+				break
+			fi
+
+			# If a library exists, blindly use it.
+			if test -f "$d/lib/libldap.so"
+			then
+				dlz_ldap_libs="-L$d/lib -lldap"
+				break
+			fi
+
+			# Start over.
+			dlz_ldap_inc="yes"
+			dlz_ldap_libs="yes"
+		done
+
+		# Done searching.  Check that everything was found.
+		if test "yes" = "$dlz_ldap_inc"
+		then
+			AC_MSG_ERROR([could not find LDAP include directory])
+		fi
+
+		if test "yes" = "$dlz_ldap_libs"
+		then
+			AC_MSG_ERROR([could not find LDAP library])
+		fi
+
+		DLZ_ADD_DRIVER(LDAP, dlz_ldap_driver, [$dlz_ldap_inc], [$dlz_ldap_libs])
+
+		AC_MSG_RESULT([using LDAP: $dlz_ldap_inc $dlz_ldap_libs])
 		;;
 esac