Increased system partition from 256M to 512M and userdata from 256M
to 1047M

Now all 2G of eMMC flash is used (on rev A/B). Must build Android images
in sparse format (remove TARGET_USERIMAGES_SPARSE_EXT_DISABLED := true
from BoardConfig.mk)
Turn on USER0 LED when fastboot command is running
Added EXTRAVERSION to Makefile to identify this as having fastboot
support for BeagleBone Black