Merge pull request #218 from kleinerm/master

PTB BETA RELEASE "Random acts of kindness" Psychtoolbox-3.0.12 - SP3

Get the Linux and Windows Screen mex file rebuilt as well.
Merge pull request #221 from kleinerm/master

Pull for small beta update.

* Gaussblob procedural shader.
* Mini 4-channel mix shader.
* Demo cleanups and refinements.
* KbQueueReserve fix.
* Some DRI3/Present prep work for Linux - not relevant yet.
Fixed buglet where SaveCalFile could crash if passed filename was short.

Signed-off-by: David Brainard <brainard@psych.upenn.edu>
Fix way that full file path is computed to use fullfile.  This is more robust.

Signed-off-by: David Brainard <brainard@psych.upenn.edu>
MergeCell did not handle empty inputs as it should (ignoring/early exit)
Merge pull request #223 from dcnieho/MergeCell_patch

MergeCell did not handle empty inputs as it should (ignoring/early exit)
Merge pull request #224 from kleinerm/master

Pull current state into public master for 3.0.12 release.

* Improve KDE multi-display + single-x-screen operation on Linux.

* Add support for high precision beampos timestamping for NVidia Maxwell gpu's (GeForce 750 Ti and later) on Linux (only needed for proprietary NVidia driver) and OSX.

* Make compatible with DRI3/Present with XOrg 1.16.3+ and Mesa 10.3+ on Linux.

* Improve GStreamer video capture, make auto-detection/validation robust on analog video frame grabbers.

* Improve dc1394 video capture engine for IIDC compliant USB-3 "USB-3 Vision" cameras. Timestamping fallback to get any at least approximate capture timestamps. Video recording fixes, performance fixes.

* Ship our own custom graphics drivers for XOrg 1.15 (Ubuntu 14.04-LTS) for intel and nouveau:
 - nouveau 1.0.11 ddx to replace unsuitable 1.0.10 ddx of 14.04.
 - intel 2.99.917 ddx, dri2 only, with patch for fixed ZaphodHead support and triple buffering disable.
 - These as stop gaps until 14.04 hopefully gets a backported 14.10 stack with fixed DRI3, ie., XOrg 1.16.3+

* New demo ImageMixingTutorial and the much simpler SimpleImageMixingDemo contributed by Natalia.

This release contains no rebuilt/improved mex files for MS-Windows, as none of the improvements benefits MS-Windows.
Merge pull request #53 from Psychtoolbox-3/master

Resync with current master of official Psychtoolbox-3 repo. v3.0.12-SP5