some changes to get the enc28j60 working with uIP
updated rs232.c to no longer user the deprcated prog_char
added differential sampling to the ADC
Merge branch 'xmega' of git://github.com/jmondi/contiki-xmega into xmega-enc28j60
getting up to date
need this value for our 25/6mhz external clock
Merge branch 'xmega' into xmega-enc28j60

Conflicts:
	cpu/avr/dev/rs232.c
	cpu/avr/dev/rs232.h
	platform/avr-poe/contiki-poe-main.c
	platform/avr-poe/dev/xmega-adc/xmega-adc.c
	platform/avr-poe/net/eth-enc28j60.c
redid the enc28j60 driver to use the standard SPI library.
reformatted the code, and added a bit to detect if something is holding the SS line low.
no need for those delays