Collect garbage before running mjsunit/fast-prototype

Collect garbage before running mjsunit/fast-prototype

When not using a snapshot, after turning on i18n, there's just enough
garbage after creating a context to trigger gc at the wrong moment.
Since the test uses natives syntax to access information that would
otherwise be hidden from javascript, this makes the test fail

BUG=none
R=mstarzinger@chromium.org
TEST=mjsunit/fast-prototype passes on ia32.release with no snapshot

Review URL: https://codereview.chromium.org/23452047

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16830 ce2b1a6d-e550-0410-aec6-3dcde31c8c00