Some more threadpool MPM changes:

- Add a "state" variable to the worker_wakeup_info struct. This is
  used to make sure that we act on the correct signal, and to know when
  to shut down a worker thread.
- Fix the call when the worker thread waits for a connection to use
  the new state variable and use mutexes around the cond_wait() call.
- Change the interrupt_all() call to set the WORKER_TERMINATED state.
- Add two AP_DEBUG_ASSERT() to make sure that we aren't waking up
  a worker thread before it is idle.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94843 13f79535-47bb-0310-9956-ffa450edef68