Minimal image size is set to 5*5 for OCL path of fastNlMeansDenoising and fastNlMeansDenoisingColored since it breaks tests with test_loop_times=30 and in general doesn't make sense for computation on GPU.

it generates warning

1. someMatrix.data -> someMatrix.prt()
2. someMatrix.data + someMatrix.step * lineIndex -> someMatrix.ptr( lineIndex )
3. (SomeType*) someMatrix.data -> someMatrix.ptr<SomeType>()
4. someMatrix.data -> !someMatrix.empty() ( or !someMatrix.data -> someMatrix.empty() ) in logical expressions

Fixed buffer initialization in reduce kernel. Enabled OCL version of reduce for SUM, MAX, MIN modes.

BUGFIX: Fixed bugged when setting PVAPI property CV_CAP_PROP_FRAME_HEIGHT.