added pause command to the jukebox example
AlsaSink: clear audio buffers on stop...

and audio discontinuity.
AlsaSink: added start and pause implementations

Conflicts:
	spotify/audiosink/alsa.py
AlsaSink: fixed memory leak

Conflicts:
	spotify/audiosink/alsa.py
AlsaSink: fixed ALSAAudioError under some conditons

bug was caused under this condition (jukebox.py):
    * play a track
    * pause
    * session.seek(0) # in the jukebox shell
    * play
    * pause
    * play
    * raises: "ALSAAudioError: File descriptor in bad state"
AlsaSink: added testcase for bug in last commit
AlsaSink: made testcase work on Travis
AlsaSink: skip alsa tests if pyalsaaudio isn't installed
Merge pull request #95 from stifal/alsa-playback-handling-2

Make AlsaSink play, pause and stop actions happen without delay even with big period_size.