Fixup PsychDefaultSetup(2) setup of normalized colorrange - do still clamp.

PsychDefaultSetup(2) only changes the color range to 0-1, but does not
change clamping state, ie., it doesn't disable framebuffer range
clamping.

Turns out if we indiscriminately disabled clamping, we would run into
problems with old graphics hardware (or less capable software
rasterizers like VirtualBox VM). If the GPU doesn't support
glClampColorARB extension, PTB would choose the shader based
fallback/emulation, which can fail on GPU's with limited or no shader
support, and then scripts would produce color artifacts! While this is
expected behaviour if one explicitely wishes to disable clamping -- one
simply has to use modern hardware in this case, it is an unexpected and
unacceptable failure mode when running on old OpenGL hardware.

Tested on a MS-Windows VM with VirtualBox, where the old approach broke
down due to limitations of VirtualBox's software rasterizer / GPU
emulation. Now works.

PsychImaging updated (code + docs), PsychDefaultSetup help text updated.
All Screen mex files for desktop platforms Linux, OSX, Windows rebuilt.

To provide PsychDefaultSetup(2) support for all but Linux mobile
(Nexus-7), which is a separate commit.
Merge branch 'master' of https://github.com/kleinerm/Psychtoolbox-3