Adds C_FAKEFORK envvar for simple init script/multi debugging

This means that you can now do:

    C_FAKEFORK=1 celery multi start 10

or

    C_FAKEFORK=1 /etc/init.d/celeryd start

to avoid the daemonization step to see errors that are not visible
due to missing stdout/stderr.

Conflicts:
	celery/bin/celeryd_detach.py