Add support for Cgywin, apparently it is enough just to open the tty again in

the server and fd passing is not necessary. Needs some ifdefs unfortunately but
no way around that and some of them can go next time we're willing to do a
protocol bump. Patch from J Raynor jxraynor at gmail dot com.

client.c

@@ -328,8 +328,13 @@ client_send_identify(int flags)
 	    strlcpy(data.term, term, sizeof data.term) >= sizeof data.term)
 		*data.term = '\0';
 
+#ifdef __CYGWIN__
+	snprintf(&data.ttyname, sizeof data.ttyname, "%s",
+	    ttyname(STDIN_FILENO));
+#else
 	if ((fd = dup(STDIN_FILENO)) == -1)
 		fatal("dup failed");
+#endif
 	imsg_compose(&client_ibuf,
 	    MSG_IDENTIFY, PROTOCOL_VERSION, -1, fd, &data, sizeof data);
 	client_update_event();