It was just a typo in the documentation.

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.

Add calculating integral image using IPP

Also, shrunk the corresponding column and the test name column.

- set init value for `numsdev` to prevent use of uninitialized value
- stop use of 'workdir' and files from samples
- forcing use of 'opencv_extra' instead
Note: set OPENCV_TEST_DATA_PATH to full path to 'opencv_extra/testdata' (gitolite@code.opencv.org:opencv_extra.git) before running the test!