Because we track the value of the arguments object, we need to check
values whenever plugged into a forbidden value context.  It is not
enough to check at only variable references as we did previously.

R=fschneider@chromium.org
BUG=1351
TEST=regress-1351.js

Review URL: http://codereview.chromium.org/6902202

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7739 ce2b1a6d-e550-0410-aec6-3dcde31c8c00