add NEON realization for StereoBM(findCorrespondence, prefilterXSobel)
Add CV_Assert (ndisp % 8 == 0) to NEON version
Merge pull request #2827 from Alexander-Petrikov-ELVEES-NEOTEK:neon-stereobm
GCC 4.8 warning array subscript is above array bounds fixed.
Merge pull request #3093 from asmorkalov:ocv_array_bound_fix
Fix reallocation of D buffer in gemm

Conflicts:
	modules/core/src/matmul.cpp
Merge pull request #3108 from LeszekSwirski:fix-gemm-buf-allocate-2.4