* nscd/nscd.c (parse_opt): Read response from INVALIDATE request
to make sure the database has been already invalidated.
* nscd/cache.c (prune_cache): Add fd argument. Write response to fd
after the cache has been invalidated. Use pthread_mutex_lock rather
than pthread_mutex_trylock if fd != -1.
* nscd/connections.c (invalidate_cache): Add fd argument, write
response to fd if not calling prune_cache, pass fd to prune_cache.
(handle_request): Adjust invalidate_cache caller.
(nscd_run): Pass -1 as fd to prune_cache.