add support for devicenumber parameter in el, this is sent to KbCheck
when calling EyelinkGetKey.m, see help for KbCheck for details on what
this does
Merge pull request #15 from iandol/eyelink1

add support for devicenumber parameter in el
Screen/GStreamer: Allow override of selection of threaded video decoding method.

For multi-threaded video decoding on capable codecs, we default to use
both slice-threading and frame-threading. An environment variable
allows to override this choice.

The variable can be set via new PsychTweak subcommand:
PsychTweak('GStreamerPlaybackThreadingMethod', methodId);

-> Screen for 64-Bit Matlab on OSX rebuilt and tested against patched
gst-ffmpeg decoder branch. Works as expected.