first experiment : no more async switches, new method to block without
blocking the event loop
[ ABSOLUTELY NOT READY ]
Get max_age to respect graceful_timemout

This an experiment towards solving #537
Some code can probably be merged with Watcher.begin_stop and Watcher._final_stop
Merge pull request #2 from amarandon/async_experiment

Async experiment with max_age
still some experiments
Merge branch 'async_experiment2' into async_experiment

Conflicts:
	circus/watcher.py
making process with stop command
start to work
add some hints
unit tests ok
set command is now asynchrounous (because of restart)
add a space for flake8/travis build
some progress
some details
exclusive locks between some commands
Merge branch 'refs/heads/command_exclusion'