Move the is_pregenerated flag so it does not overlap other flags.

Move the is_pregenerated flag so it does not overlap other flags.
Remove the before-or-after InstanceOf stub rule, which was too
subtle and lacked checking ssertions.
Unify the way the CEntry stub is pregenerated so that it is done
in the same way.
Review URL: http://codereview.chromium.org/8065006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9466 ce2b1a6d-e550-0410-aec6-3dcde31c8c00