This is Update 1 to the AT90USB Arduino

BOOTLOADERS:
Added support for the Atmel AT90USBKey. This includes a new bootloader.
Streamlined the bootloader for the AT90usb646/7 and AT90usb1286/7. After
upload the MCU will restart more reliably.

CORES:
Fixed a bunch of issues with the Hardware Serial and USB interface. Now
supports Serial over USB and the UART functions correctly.
Most changes came from the MattairTech core.

Boards.txt added AT90usbKey support.