Bailout to JS Array builtins if array's prototype is different from
Array.prototype.  Otherwise there might be inherited elements coming
from this prototype.

Review URL: http://codereview.chromium.org/2037008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4649 ce2b1a6d-e550-0410-aec6-3dcde31c8c00