Make the implementation of GPrivate behave more closely as in POSIX

Make the implementation of GPrivate behave more closely as in POSIX

2006-02-20  Tor Lillqvist  <tml@novell.com>

	* gthread-win32.c (g_thread_exit_win32_impl): Make the
	implementation of GPrivate behave more closely as in POSIX
	threads: The value associacted with a GPrivate must be set to NULL
	before calling the destructor. (The destructor gets the original
	value as argument.)  A destructor might re-associate a non-NULL
	value with some GPrivate. To deal with this, if after all
	destructors have been called, there still are some non-NULL
	values, the process is repeated. (#331367)