Fix doxygen comment in BFMatcher

numpy 1.13.0+

- '-fvisibility' flag was updated
- PVAPI library detection was changed

Fixing explicitly call download method for cuda::GpuMat object

[GSOC] Enable OCL for AKAZE (#9330)

* revert e0489cb4 - reenable OCL for AKAZE

* deal with conversion internally in AKAZE

* pass InputArray directly to AKAZE to allow distiguishing input Mat/UMat. deal with conversion there
* ensure that keypoints orientations are always computed. prevents misuse of internal AKAZE class.

* covert internal AKAZE functions to use InputArray/OutputArray

* make internal functions private in AKAZE

* split OCL and CPU paths in AKAZE

* create 2 separate pyramids, 1 for OCL and 1 for CPU
* template functions that use temporaries to always store them as correct type (UMat/Mat)

* remove variable used only in OCL path

causes unused variable warning

* update AKAZE documentation

* run ocl version only when ocl is enabled

* add tests for OCL path in AKAZE

* relax condition for keypoints angle

Version: gcc (GCC) 7.1.1 20170622 (Red Hat 7.1.1-3)
Flags: -fsanitize=address,undefined