Added fix to OpenCVFindMatlab.cmake to properly locate modern versions of unix- MATLAB.  Tested with MATLAB R2015a and Ubuntu 14.04.

Command 'execute_process' from OpenCVFindMatlab module can omit error message
to the standard output. This can break build of the OpenCV package in
ExternalProject_Add (Windows/Visual Studio).

Streamlined mexext detection, with removal of trailing whitespace/newlines handled by execute_process

Improved finding Matlab on Windows machines. Needs testing on computers that have multiple version installed

Added basic ability to find Matlab installations. Added test cpp file under modules/matlab/test to test mex compiler within cmake