Full "git describe" and username in version string

Include full "git describe" output and username in version string for
easier tracking.

Examples:

uloader 2011.06.0-gfiber-38.2-6-gc15f86d-dirty-da (Apr 16 2014 -
16:39:11)

barebox 2011.06.0-gfiber-38.2-6-gc15f86d-dirty-da (Apr 16 2014 -
16:39:35)

Change-Id: I027c57e8af60afb7492e00e8e7623bd01a21d325
2 files changed