make standard regexps like \s and . case independent.
* Make use of the fact that the subject string is ASCII only
when making character classes case independent.
* Avoid spending time making large ideogram or punctuation
ranges case independent when there is no case mapping anyway.
Review URL: http://codereview.chromium.org/378024

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3243 ce2b1a6d-e550-0410-aec6-3dcde31c8c00