Add array bound checks to code generated for SwapElements. This fixes a bug that lead to a segfault when an array was modified while it was sorted.

Review URL: http://codereview.chromium.org/5686006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6020 ce2b1a6d-e550-0410-aec6-3dcde31c8c00