evdevtouch: Disable threading.

This should never have been threaded. It isn't resource-intensive, and it needs
to communicate touches back to the main thread anyway.

Removing the threading significantly(!) improves latency.
evdevtouch: Don't try to keep reading if we get EAGAIN.

This stops touching the screen (and not moving) consuming 80-90% CPU. :)
Merge pull request #4 from rburchell/evdevtouch

Improve touch responsiveness and latency.