Added a simple new space check on the elements fixed array which can allow
updating with other values than smis without updating the remembered set.

Also combined the positive smi and range check so that a separate smi check can be avoided when the key is known to be a smi.

This is a port of r4543.
Review URL: http://codereview.chromium.org/1702013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4547 ce2b1a6d-e550-0410-aec6-3dcde31c8c00