Strict mode flag is passed to runtime DELETE function
and then to JSObject::Delete(Property/Element) as STRICT_DELETION enum.
When deleting non-configurable property/eleemnt, TypeError is thrown.
Adding mozilla test to .gitignore.
Incorporate CR feedback.

Review URL: http://codereview.chromium.org/6515005/

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6782 ce2b1a6d-e550-0410-aec6-3dcde31c8c00