Resolve opt_vardir in MTR with realpath. Server resolves some directory names, thus

mtr should do it as well, to avoid differences in test output. 

This fixes sys_vars.secure_file_priv on FreeBSD9.0 buildbot.

mysql-test/mysql-test-run.pl

@@ -79,6 +79,7 @@ BEGIN {
 use lib "lib";
 
 use Cwd ;
+use Cwd 'realpath';
 use Getopt::Long;
 use My::File::Path; # Patched version of File::Path
 use File::Basename;
@@ -1040,8 +1041,14 @@ sub ignore_option {
 # Setup any paths that are $opt_vardir related
 sub set_vardir {
   my ($vardir)= @_;
-
+  if(IS_WINDOWS)
+  {
     $opt_vardir= $vardir;
+  }
+  else
+  {
+    $opt_vardir= realpath($vardir);
+  }
 
   $path_vardir_trace= $opt_vardir;
   # Chop off any "c:", DBUG likes a unix path ex: c:/src/... => /src/...