in order to make CMake scripts work properly

VideoCapture didn't call release method and just ignored the new capture sources.
OpenCV documentation:
  bool VideoCapture::open(const string& filename);
  bool VideoCapture::open(int device);

The methods first call VideoCapture::release() to close the already opened file or camera.

Conflicts:
	modules/features2d/include/opencv2/features2d/features2d.hpp
	modules/ocl/src/opencl/stereobp.cl
	modules/ocl/src/stereobp.cpp