- Added fast case to String.prototype.split (Mads's idea).
- Made minor other optimizations in String.prototype.split.

Review URL: http://codereview.chromium.org/126201

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2191 ce2b1a6d-e550-0410-aec6-3dcde31c8c00