Screen: Be more clever about 10 bpc framebuffers.

Check if a bpc=10 requested native framebuffer is set up 10 bpc via
query to OpenGL context. Only fallback to PsychtoolboxKernelDriver /
MMIO tricks, or eventually fail, if that is not the case.
This makes detection of need for MMIO fallback on Linux more clever.
This makes detection of need for PsychtoolboxKernelDriver fallback on
OSX more clever, as it at least tries to get 10 bpc from the OS, before
falling back to our own solution. Note that as of OSX 10.8, 10 bit
native framebuffers are still not supported, and likely this will also
be the case for the upcoming 10.9 Mavericks. This change in code is
just to make us behave intelligently if Apple ever decided to honor
requests by its customers.

Also fix handling of AGL conserveVRAM settings for OSX in 'OpenWindow'.
Screen/OSX: Drop support for AGL + Carbon, cleanup Cocoa path.

This removes all support for AGL + Carbon windows, and for OSX 10.5
Now we always use CGL for OpenGL, and for windowed mode or
half-transparent windows, we use CGL wrapped into NSOpenGL contexts +
windows created by Cocoa. This allowed for a nice cleanup of the
PsychCocoaGlue.c and PsychWindowGlue.c files.

-> Screen for 64-Bit Matlab and Octave on OSX rebuilt and tested.
Screen: Make GStreamer the default videocapture engine on all OSes.

So far the default was different on 32-Bit OSX, but this is now
unsupported.
Screen/OSX: Split vbl timestamping into separate shm and cvdisplaylink

Disentagle both mehods, so one can work without the other:
Only good old and reliable iofb shmem vbl irq timestamping on 10.6.
Only new and crappy CVDisplayLink timestamping on 10.7 and later.

Screen for OSX rebuilt.
Screen/OSX: Disable screen release/capture hack for cgl windows.

The hack was to release a captured display, then CGLClearDrawable to
detach the OpenGL context from the display, then capture the display
again. This was to fix some display corruption in stereo display mode
on OSX 10.5.x

As 10.5 is no longer supported, remove the workaround and just
CGLClearDrawable().
Fixes some warning messages in system log on 10.7.

-> Screen for OSX rebuilt and tested.