Speed up access to global variables from eval scopes. Traverse the

Speed up access to global variables from eval scopes.  Traverse the
surrounding context to figure out if the variable could be global.  If
the variable could be global we check context extension objects at
runtime and use a global LoadIC if no variables have been introduced
by eval.

Fix crash bug when loading function arguments from inside eval.  The
shadowed variable in the DYNAMIC_LOCAL case does not rewrite to a slot in
that case.

Review URL: http://codereview.chromium.org/28027

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1348 ce2b1a6d-e550-0410-aec6-3dcde31c8c00