pdf2john: allow symlinked usage by resolving script path

This resolves the script's real path which is then used to populate
the perl module include path to the appropriate location of the
vendored lib folder.
This allows using pdf2john anywhere as a symlink, f.e. inside $PATH.

Fixes openwall#4089

run/pdf2john.pl

@@ -24,10 +24,11 @@
 my $version = '8.99';
 
 # add our 'lib' directory to the include list BEFORE 'use ExifTool'
+use Cwd qw(realpath);
 my $exeDir;
 BEGIN {
     # get exe directory
-    $exeDir = ($0 =~ /(.*)[\\\/]/) ? $1 : '.';
+    $exeDir = (realpath($0) =~ /(.*)[\\\/]/) ? $1 : '.';
     # add lib directory at start of include path
     unshift @INC, "$exeDir/lib";
     # load or disable config file if specified