BF: iohub keyboard release event

auto_repeated field being set to None on Linux when the key was not
found in the pressed_events dict.
Merge branch 'master' of git://github.com/psychopy/psychopy
ENH: iohub process and client connection updates

+ Added enableRealTimePriority  and disableRealTimePriority methods to
ioHubConnection class

+ ioHubConnection should now be using a standard python socket to
connect to the iohub server. It was using a gevent socket, which was
unnecessary, and caused issues when ioHubConnection instance was created
in main thread and events were accessed in another thread.
ADD: Demo to test impact of process priority

as well as python garbage collection. I had made this extension when the
whole process priority stuff came up a month ago or so. Not sure if you
want to keep it or toss it. Up to you.

+ Added some more file extensions that github should ignore.
REM: Removed Cobra eye tracker imp.
Merge pull request #766 from isolver/master

BF: iohub keyboard release event auto_repeated field can be None on Linux