oebb.sh: test for git 1.8 and fall back to old test if older

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
oebb.sh: pass bitbake error code back to shell

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Merge pull request #34 from Angstrom-distribution/angstrom-v2012.05-yocto1.2

Angstrom v2012.05 yocto1.2