- that way __del__ on local is not necessary

monkey: make patch_thread() use gevent.local.local; also make it explicitly set threading.local and _threading_local.local

coros: reimplement Semaphore similarly to how Event is implemented; add rawlink() and wait() methods

- add DummySemaphore class

http://code.google.com/p/gevent/issues/detail?id=24

- it's no longer used by gevent itself