GPUFFTVideoCaptureDemo: Don't keep resources mapped during OpenGL operation.

I had 2nd thoughts about this and now opt for "Better safe than sorry"
by default:

% At least on Linux + NVidia + CUDA-5.0 it is currently safe to keep
% texture resources mapped during OpenGL operations on CUDA-OpenGL
interop
% textures. On Windows we don't know yet. On OSX it is a total no-go.
However,
% the CUDA-5.0 programming guide strongly advices against keeping
resources
% mapped during OpenGL operations, as the "results of such actions will
be
% undefined". In other words, nothing guarantees it will work, or even
if it
% works now, will continue to work in the future. So better safe than
sorry
% and default this to off on all platforms. Adventureous or performance
% desparate users can enable it on their system and see if it works.