Screen: Allow use of multisample textures for multisample anti-aliasing.

If GL_ARB_texture_multisample extension is supported, then preferrably
create and use multisample textures as color attachments for the
imaging pipeline drawBufferFBO's if multisampling is requested. Only
fallback to good ol' multisampled renderbuffers if textures fail or are
unsupported.

Multisample textures have the advantage that they can be used with the
imaging pipelines identity blit chain, and thereby by the panelfitter
fallback code. This should allow to provide framebuffer rotation for
multisampled framebuffers via the panelfitter.

It also provides yet another fallback for multisample resolve if scaled
multisample resolves are not supported.

So far the theory. In practice the code-path is only compile-tested,
because Apple's crappy os doesn't expose the needed extension under
OpenGL 2.1, despite the gpu being perfectly capable of supporting it.
-> Will need reboot to a real os for testing.
Screen: Disable beamposition queries for Intel gpu's under OSX and Linux.

In light of the latest insights about Intel hw design defects and
possible hard lockups/crashes of Intel chipsets if register reads
aren't serialized on the gpu, use of our homegrown beamposition
implementation via MMIO register direct access is no longer safe, as we
can't serialize access with the os kernel graphics driver.

-> Disable use of PsychtoolboxKernelDriver instances for Intel on OSX
and of direct mmap() MMIO mapping on Linux. This can be overriden via
setenv('PSYCH_ALLOW_DANGEROUS', '1') for testing by the really brave.

-> This is no loss on Linux, as the DRI2/Intel-KMS graphics driver
provides high quality OpenML timestamping anyway.
-> This is a kiss of death on OSX for Intel GPU's if precision timing
is needed, as OSX CGDisplayBeamposition() is not and was not ever
supported on Intel IGP's.
-> On MS-Windows we can continue to use DirectDraw GetScanLine() in the
hope that the MS-Windows Intel gpu drivers properly serialize their
accesses. However, the most likely implementation they have chosen will
make beampos queries less robust and accurate, thereby reducing the
effectiveness of beampos timestamping on Windows as well.

-> Linux as the last bastion of Intel graphics for vision science.
Rebuild ftgl drawtext text rendering plugins for desktop Linux and OSX.

32/64-Bit Linux, 64-Bit OSX rebuilt with latest enhancements.
Screen mex file for all desktop platforms rebuilt.

All except Linux+ARM. This syncs up panelfitter enhancements,
multisample texture support, Intel GPU disablement, Drawtext plugin
support etc.
PanelFitterDemo: Add test code for multisampling + rotation.

For testing on Linux. We know the fallbacks and error handling work,
but not yet if multisample textures bring the expected advantages of
MSAA + framebuffer rotation.
-> Test pending.