Initial riak support
Add some documentation on class attributes

Also add handling of protocol.
Cleanup code related to connection to Riak

This is a leftover of previous work on this backend.
Switch default bucket name to celery
Add riak to extra requirements
Add Riak backend documentation
Fixed error in protocol handling for the riak backend
Use a heapq to avoid calling all entries for every iteration
Remove print
Fixes broken rst ref.  Closes #1998
Travis: Only get IRC notification when build fixed and failed
Support of missing CELERY_BIN and CELERY_APP, described in http://celery.readthedocs.org/en/latest/tutorials/daemonizing.html#id11
Added centos celerybeat init script + sysconfig example + simple tests
Worker --detach must forward working_directory option.  Closes #2003
New signals: app.on_configure, .on_after_configure, .on_after_finalize
Fixes bugs with bootsteps: requires attribute not inherited by subclasses and using module paths did not work properly.  Closes #2002
Fixed wrong arguments
Merge pull request #2007 from malinoff/fix-worker-argv-run

Fixed wrong arguments passed to maybe_detach
Fixes tests
Stresstests: envvar C_SLEEP can now be used to add tracebacks to sleep calls