shifts by zero or arithmetic shifts.  Updated to also
eliminate ASR followed by LSL as per part two of
http://codereview.chromium.org/1987008/show
Review URL: http://codereview.chromium.org/2054007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4641 ce2b1a6d-e550-0410-aec6-3dcde31c8c00