PsychHomeDir: Fix weirdo failure on Matlab 7.4 + 1 Linux system.

Failed on 12.04 LTS with Matlab R2007a, nowhere else. Weird,
but just increase robustness a bit and we're fine again.
memcpyCudaOpenGL: Rename to C++ type, make it build on 64-Bit Linux.

Add support for 64-Bit Matlab on Linux. This needs switching from
C to C++ compile, although we don't use anything C++, but due to
a small bug in the CUDA-5.0 SDK for Linux (one of the header files),
that CUDA header file won't compile in pure C mode, although it is
supposed to. Simple fix: Compile our C file with the C++ compiler.

Also cleaned up all remaining bits of C++'isms in the source code.

-> memcpyCudaOpenGL.mexa64 is the new Linux mex file.
-> Tested on Ubuntu 12.04.1 LTS with CUDA-5.0 on GeForce-8800 Ultra.

Suspicion was right: Our code does things properly and (un)mapping
of OpenGL resources and async data copy is highly efficient on Linux,
yielding memory bandwidth utilization > 90% of the theoretical peak
performance of the GPU.

Ergo all the observed awful slowness is just due to the mind-blowing
poor performance of the MacOSX 10.7.5 graphics system. Running on
Linux yields close to a 100x performance gain for OpenGL-CUDA interop!
The "most advanced operating system in the world" takes things at its
own pace lol...

Still, benchmarking shows a significant performance impact due to
the register/unregister calls for OpenGL graphics resources, so these
should be avoided as much as possible. Seems i do need to implement
some fancy LRU caching scheme to reduce those calls, but only after
a good night of sleep...