Add explicit support for the AT90USB646 to the Teensy bootloader now that PJRC have released the Teensy++ board.
Ensure unfinished SideShow demo uses an unallocated PID value within the LUFA range.
Changed USB_Init() and USB_Shutdown() so that they are no longer dependant on oneanother for possible code savings when the interface is never explicitly shut down.
Fixed incorrect ENDPOINT_EPNUM_MASK mask preventing endpoints above EP3 from being selected (thanks to Jonathan Oakley).
Removed STREAM_CALLBACK() macro - callbacks now use regular function definitions to clarify user code.
Removed DESCRIPTOR_COMPARATOR() macro - comparators should now use regular function definitions to clarify user code.