PsychHID/Linux: Change default debug level for libusb to zero = silence.

So far we had highest level of verbosity by default (3), which caused
significant spilling of meaningless warning and error messages which
didn't point to any real problem.

Now we default to silence. Usercode can still enable verbose debug
output by calling PsychTweak('LibUSBDebug', verbose) with a verbose > 0
level before first invocation of PsychHID, should there be a need
for low-level debugging of problems. The function influences all uses
of libusb-1.0 based mex files loaded after the PsychTweak() call, e.g.,
also PsychKinectCore, some libdc1394 usb video capture, etc.

-> PsychHID mex file for 32/64-Bit Matlab/Octave on Linux rebuilt.
-> PsychTweak() extended.