A possible fix for bug #14333 with hanging at exit on MS-Windows.

A possible fix for bug #14333 with hanging at exit on MS-Windows.

 src/w32.c (term_winsock): Call release_listen_threads before calling
 WSACleanup.
 (_sys_wait_accept): Wait for accept event in a loop with a finite
 timeout, instead of waiting indefinitely.  Will hopefully avoid
 hanging during exit because WSACleanup deadlocks waiting for the
 event object to be released.
 src/w32proc.c (release_listen_threads): New function, signals all
 the reader threads that listen for connections to stop waiting.
 src/w32.h (release_listen_threads): Add prototype.