For redeclarations of variables that alias the parameters in functions
using arguments, we need to avoid re-visiting the shared variable
rewrite.

BUG=v8:1104

Review URL: http://codereview.chromium.org/6453004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6679 ce2b1a6d-e550-0410-aec6-3dcde31c8c00