Fix issue 191:...

Fix issue 191:

    http://code.google.com/p/v8/issues/detail?id=191

Accessor setters should not be called for eval-introduced context
extension objects.

This change fixes the issue, but I think it is time to separate out
the lookup routines for eval-introduced context extension objects.
There is no reason to use the general lookup routines for this.  I'll
do that in a separate changelist.

Committed: http://code.google.com/p/v8/source/detail?r=1076

[Christian Plesner Hansen, 2009-01-15 11:29:59]

Lgtm