available.  We use this to ensure that snapshots on MacOSX can
use SSE2 instructions.  Also clean up and assertify the
handling of things we can't do when we are generating a
snapshot.  Fix a bug in the new serialization tests where
they activated Snapshot::enable() too late after code had been
generated that assumed no snapshots.
Review URL: http://codereview.chromium.org/391051

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3301 ce2b1a6d-e550-0410-aec6-3dcde31c8c00