Makefile: Show error if target pep8 fails.
Makefile: Show error if target pep8 fails.

frac/celery,WoLpH/celery,mitsuhiko/celery,frac/celery,cbrepo/celery,WoLpH/celery,ask/celery,ask/celery,mitsuhiko/celery,cbrepo/celery