Omni-0.5.1 released

- Changed the default build to retail.
- Added initial support for a pluggable blitter class.
- Added 28 new HP LaserJet class devices.
- Added 21 new Brother LaserJet class devices.
- Added 12 new Epson LaserJet class devices.
- Added 45 new Kyocera LaserJet class devices.
- Fix capabilities bug in HP LaserJet devices (thanks to terry@beam.demon.co.uk)
- Merged Red Hat's patches back into Omni.