Auto-detect true framebuffer bpc on AMD + Linux Native16Bpc support.

Add new logic to Screen() to expose the new subfield 'GPUMinorType'
in Screen('GetWindowInfo', win); queries. The field contains the
vendor specific gpuMinorType, or -1 if query is unsupported. The
meaning of the numeric id is subject to change without notice, but
currently it means the chip family id (hexadecimal) for NVidia
gpu's and the DCE display engine version (decimal) on AMD gpu's,
e.g., 40 on AMD = DCE-4.0 engine or later.

-> Screen.mex for 64-Bit Octave on Linux rebuilt for testing.
-> PsychtoolboxKerneldriver won't get a rebuild at this point,
   as we can't make good use of this new feature atm. on OSX.

PsychImaging uses the AMD GPUMinorType to decide if it should
encode for a AMD display pipeline of 10 bpc or 12 bpc true depth.

DCE-8.0 and later "Sea Islands+" gets 12 bpc, older engines get
10 bpc in 'EnableNative16BitFramebuffer' mode. Now anything less
than 12 bpc is useless in practice, as our Native10/11Bit support
can do that much more efficiently without need for special setup,
but we leave this, so we can at least test the involved code on
older than DCE-8 gpu's. Atm. i don't have any DCE-8 gpu, nor any
12 bpc display device, so the code wasn't actually tested at its
useful 12 bpc bit depth in practice. But testing on a DCE-4 card
at 10 bpc via analog VGA 10 bpc output shows the current
implementation works at 10 bpc and is expected to work on a true
12 bpc capable card and display.

-> 16Bit code successfully tested in single-display mode and
   dual-display clone/mirror mode.

-> The M/GLSL code needs some additional refinement to work on
   dual-display side-by-side "dual display stereo" configurations
   in a useful manner.