make gen_template.pl work from anywhere with FindBin

testing/mochitest/gen_template.pl

@@ -10,17 +10,17 @@
 #  perl gen_template.pl -b 345876 -type xul
 #
 #  sends a test case template for bug 345876 to stdout
-
+use FindBin;
 use Getopt::Long;
 GetOptions("b=i"=> \$bug_number,
            "type:s"=> \$template_type);
 
 if ($template_type eq "xul") {
-  $template_type = "static/xul.template.txt";
+  $template_type = "$FindBin::RealBin/static/xul.template.txt";
 } elsif ($template_type eq "xhtml") {
-  $template_type = "static/xhtml.template.txt";
+  $template_type = "$FindBin::RealBin/static/xhtml.template.txt";
 } else {
-  $template_type = "static/test.template.txt";
+  $template_type = "$FindBin::RealBin/static/test.template.txt";
 }
 
 open(IN,$template_type) or die("Failed to open myfile for reading.");