xum1541: Fixed compilation with recent avr-gcc releases.

- Declared PROGMEM variables as const.
- Removed -Werror to ignore warnings in the LUFA source
xum1541: Added teensy2 board.

The Teensy 2.0 USB Development Board is a very small, low-cost
board with an ATMEGA32U4 controller. It's available from

  http://www.pjrc.com/teensy/

No additional components are required - all the IEC lines can be
soldered directly to the board.
xum1541: Added hex files for the teensy2.

compiled with avr-gcc.exe (AVR_8_bit_GNU_Toolchain_3.4.2_939) 4.7.2