Add a patch to fix warning about character-class string.
Why patch needed? According ruby 1.8 language definition, even if
the first character-class string is square branket, warn if not
escaped with backslash. See also ruby/regex.c rev 1.81(*1). Since
[\]] is properly processed by ruby 1.6, patch this unconditionally.
Adviced about ruby language by: knu, hrs