not understood by WinSock.
(fhandler_socket::sendto): Ditto. If WinSock sendto() returns
WSAESHUTDOWN, change errno to EPIPE and raise SIGPIPE if MSG_NOSIGNAL
isn't set in flags.
* include/cygwin/socket.h: Define MSG_WINMASK and MSG_NOSIGNAL.
* include/cygwin/version.h: Bump API minor number.