TESTPAT (regex)

   Synopsis:
      TESTPAT checks the validity of a pattern.
         
   Notes:
      'regex' is a Perl regular expression like "orc", "^orc" or "^orc (.*)$".
         If it's a valid pattern, TESTPAT returns 1; if it's an invalid pattern
         (or if 'regex' is an empty string), returns 0.
      See also the help for TESTPAT$ which, for an invalid patterns, returns a
         string value containing the Perl error message. 

   Compatibility:
      Since Axbasic v1.001
