INPUT: Restore joystick support.

Back in 2013, as part of transitioning to SDL to handle all platform-specific I/O, support for joystick-style input devices was removed and not converted over.

This checkin restores joystick-style input support via the SDL APIs. This is essentially a straight restoration of the original joystick support mechanism. While admittedly klunky, it is fully compatible with the original Quake framework (except as noted below), and any old config files you happen to have laying around should work without modification.

Changes: - Added 'joyindex' cvar, which specifies the index number of the SDL joystick device you want to use. Original code was hard-coded to device zero; default value of this cvar is zero. - Originally, joystick POV/hat switch events were mapped to keycodes AUX[29-31]. Now they have their own keycodes: 'JOYPOV{UP,RT,DN,LT}'. - Due to a coding bug, the first four joystick buttons were mapped to the keycodes "JOY[1-4]", but everything after that was mapped to "AUX5" and beyond. Now joystick buttons beyond the first four are mapped to AUX1+, as appears to have been originally intended. - The previously implicit limit of 32 joystick buttons is now silently enforced.

Hello @ewhac ,

I know that it has been a while since this PR was submitted. But what is now the current status of this development?

Closing as no response from author.

Just a quick note to apologize for not responding to your messages earlier. Thank you for accepting the change.