* dbus/dbus-threads.[hc]: Documentation improvements. Clarify how
	condition variables relate to recursive mutexes.

        * dbus/dbus-sysdeps-pthread.c, dbus/dbus-sysdeps-win-thread.c,
	dbus/dbus-threads.c: Split the platforms-specific thread
	implementations into their own files.

	* dbus/dbus-sysdeps-pthread.c
	(_dbus_pthread_condvar_wait_timeout): invert the return value, it
	was backward. Not that anything uses it.