We now conform to ES5 by not deleting variables that occur in a scope
shadowed by with or eval.

Review URL: http://codereview.chromium.org/6376009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6445 ce2b1a6d-e550-0410-aec6-3dcde31c8c00