Fixed a bunch of memory leaks in tests, including:

Fixed a bunch of memory leaks in tests, including:
 - String traversal test data (now in a zone)
 - Debug message thread (now joined on exit)
 - Threading test threads (now joined on exit)
 - Changed message tests framework to cope with valgrind
Also, fixed a bug where we'd try to delete stack-allocated objects
when tearing down v8.  Good times.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1622 ce2b1a6d-e550-0410-aec6-3dcde31c8c00