r18584: found one of the fd leaks. The registry backend was using a

r18584: found one of the fd leaks. The registry backend was using a
talloc(NULL, xxx) to allocate the registry context. That had two
consequences

1) it was a massive memory leak, as all winreg operations leaked their
   entire context (including an open ldb database) every time

2) event_context_find() never found the exsting event context, so we
   used a new event context each time, which called epoll_create()
   each time, which caused a fd to be allocated
(This used to be commit 1c0a3de39828b43149d8981fc7f10e7c8b59a392)