Log Message:
Update xmame to 0.68.1.

Changes since 0.67.2 include:
- Almost everything from MAME 0.68.
- Fixed the analog joystick support so that the Y-axis is
  recognized as analog.  (Sebastien Devaux)
- The command line is now parsed even if the display cannot be
  opened.  (Christopher Stone, David Mitchell)
- Added support to the core for 4-button mice and 10-button
  joysticks.  (Ben Collins)
- Fixed several problems and did a lot of cleanup in the XInput
  code, especially for the output (e.g., showing detection
  status.  (Ben Collins)
- Fixed a few problems with -listinfo output.  (Andrea Mazzoleni)