Support already exists for grabbing the mouse in windowed mode by pressing Control-F5. This patch adds support for grabbing the keyboard by pressing Control-F6.
This is useful to me because I have a real Macintosh keyboard and prefer to use the real Command key as the emulated Command key, but I also use the Command key for hotkeys in my window manager. I spent an entire day failing to find a way to tell my window manager to stop intercepting Command key presses meant for Basilisk II, and five minutes making this patch.
Unlike with mouse grabbing, this patch does not provide an indication in the titlebar that the keyboard has been grabbed. I actually do want to leave the mouse ungrabbed when I grab the keyboard, but it may cause problems for most people; for instance, using the mouse to focus another window without ungrabbing first leaves the keyboard in a grabbed state. I can resubmit, if necessary, with any or all of these issues fixed.