Thanks to Bamm Gabriana for the info.

rpcrt4: Use an alertable wait in rpcrt4_protseq_np_wait_for_new_connection to fix a small memory leak flagged by Valgrind.

This is called only by the RPCRT4_server_thread so we don't have to 
worry about application user APCs being run at improper times.

Destroy the windows that have been created when they are no longer needed.