Merge pull request #1726 from ionelmc/patch-2

Update CONTRIBUTORS.txt
Do not apply eventlet/gevent patches to celery multi.  Closes #1717
Must keep maxtasks * 4 events in heap
Tests passing
events.State now supports callbacks for on_node_join/on_node_leave, also fixes #1728
Chord join must use with allow_join_result()
Fixes Redis backend
Chord unlock must be called after header.  Closes #1700
unlock_chord task should raise Retry
Fixes typo
Use sudo with rabbitmqctl
Properly set warnings.warn stacklevel
Generic init script: Use su to set user (means CELERYD_GROUP no longer will be used to set group).  Closes #1578
Beat init script now also uses su (and more improvements). Closes #1578
Celery.close should not create amqp object if not already created
Fixes outdated links in supervisord examples.  Closes #1733
To APP
Worker: Pidfile, logfile and statedb arguments now supports %n/%h formats
Adds prefetch multiplier and prefetch count to glossary
Fixes name error