r6635: Remove the redundant load on every context lookup.
r6659: Do not compile the unreachable body of functions with illegal redeclarations.
Review URL: http://codereview.chromium.org/6572003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6920 ce2b1a6d-e550-0410-aec6-3dcde31c8c00