Corrected documentations to include .gb files

test.pl also accepts .gb files (GOTO binary programs), amending the main
source documentation to reflect this.

Author: thk123

regression/test.pl

@@ -194,7 +194,7 @@ ($$$$)
 
 where
   <level>                is one of CORE, THOROUGH, FUTURE or KNOWNBUG
-  <main source>          is a file with extension .c/.i/.cpp/.ii/.xml/.class/.jar
+  <main source>          is a file with extension .c/.i/.gb/.cpp/.ii/.xml/.class/.jar
   <options>              additional options to be passed to CMD
   <grep_options>         additional flags to be passed to grep when checking required
                          patterns (this is optional, if the line stats with a `-'