Replace select() usage for a Poller class witch uses either kqueue(), poll() or select() backend

This patch aims to fix the issue #26.

The Poller() class uses kqueue() or poll(), if available, with a fall back to select() (witch remains with problem). 

I've tested with this config file: http://ideone.com/sH2Z7 :

`sudo bash -c "launchctl limit  maxproc 2048 2048 ; supervisord -nc sample-cat-stress.conf"`

Both poll() and kqueue() work as expected. But select() raises (as reported on #26):

`ValueError: filedescriptor out of range in select()`