Build and tests should work when APR doesn't support threads.

* auth/auth.c
  (cleanup_user_scheme): Don't call init_authn_schemes_guard() explicitly.

* test/MockHTTPinC/MockHTTP_server.c
  (run_thread): Define function only if APR supports threads.
  (mhStartServer, mhStopServer): Move threading-specific local variables
   inside the APR_HAS_THREADS conditional block.


git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1931478 13f79535-47bb-0310-9956-ffa450edef68