Fix a bug in a corner case of direct eval detection.

Fix a bug in a corner case of direct eval detection.

The corner case is calling a function named 'eval' that is looked up at
runtime and found in a non-global context (but not an extension object).
The bug is that we used the function itself as the receiver rather than
using the global object.

R=ager@chromium.org
TEST=has been added to the eval mjsunit test

Review URL: http://codereview.chromium.org/6893057

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7696 ce2b1a6d-e550-0410-aec6-3dcde31c8c00