PTB BETA RELEASE "Random acts of kindness" Psychtoolbox-3.0.12 - SP5

* 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 "show off" demo ImageMixingTutorial, and the much cleaner/simpler SimpleImageMixingDemo contributed by Natalia Zaretskaya.

* Bug fix to MergeCell() by Diederick Niehorster.

* Bug fix to SaveCalFile() by David Brainard.

This release contains no rebuilt/improved mex files for MS-Windows, as none of the improvements benefits MS-Windows.