I have seen that you can input a Mat_<float> on StereoBM, but the value seems the same as CV_16S.
I changed it so, only if you input a Mat_<float> it makes use of a previously truncated 4 bits, giving more resolution to Disparity Matrix. (The algorithm stays the same, it's not more precise).
If any other input Mat is given, it changes nothing.

in this case the sample will not be built if OpenGL is not found

  * use SSE and/or AVX based on configuration
  * revise the test to verify the implementation