interceptors and dont-delete attributes.

Minor change to the behavior of eval: throw exception when calling
eval in a context for which the global has been detached.  This
matches the behavior of both Firefox and Safari post navigation in the
browser.
Review URL: http://codereview.chromium.org/118374

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2118 ce2b1a6d-e550-0410-aec6-3dcde31c8c00