avr/bootloader.c: Now compatible with bootloaders which always run first.

The boot loader now knows when to go into bootstrap mode by
looking for a specific EEPROM value. Also updated code style
to match Contiki code style guidelines.
Merge pull request #153 from darconeous/pull-requests/cpu-avr-bootloader

avr/bootloader.c: Now compatible with bootloaders which always run first