Instead, create Local handles to pass them around. This also means that the
code needs to be shifted around a bit such that a handle scope exists when
creating threads.

Review URL: https://codereview.chromium.org/14150017

Patch from Jochen Eisinger <jochen@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14420 ce2b1a6d-e550-0410-aec6-3dcde31c8c00