Replaced the keyword matching state machine with a switch on the first char followed up by inlined char comparisons.

R=lrn@chromium.org
TEST=cctest/test-parsing/ScanKeywords

Review URL: http://codereview.chromium.org/7558017

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8866 ce2b1a6d-e550-0410-aec6-3dcde31c8c00