Avoid the KMP overhead for simple indexOf() operations.  Will look into evaluating the best cutoff between a simple search and KMP in the future.  This improves some simple operations ~1.5x.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@349 ce2b1a6d-e550-0410-aec6-3dcde31c8c00