* Use Sys_Sleep to limit FPS, which will save CPU

* Add com_maxfpsUnfocused and com_maxfpsMinimized; self explanatory
* Fix reopening of bug 3703, I hope

code/sys/sys_unix.c

@@ -463,6 +463,9 @@ void Sys_Sleep( int msec )
 {
 	fd_set fdset;
 
+	if( msec == 0 )
+		return;
+
 	FD_ZERO(&fdset);
 	FD_SET(fileno(stdin), &fdset);
 	if( msec < 0 )