continue fixing nonfree elements
fixed dependency of stitching module on xfeatures2d module as optional
fixed the initModule_xfeatures2d function that was called in module stitching since it is in another namespace than the standard cv one.
Disabled native_sqrt for double, since it may be not implemented and gives compilation error.
Merge pull request #3163 from StevenPuttemans:fix_nonfree_items
OCL: enable clAmdFftGetVersion
fix for cv::memopTypeToStr
Added check AmdFft version to be sure that AmdFft binaries are available
attempt to fix compilation of OpenCL cv::transpose for AMD
Merge pull request #3172 from ilya-lavrenov:tapi_transpose_amd
Merge pull request #3171 from akarsakov:amd_fft_fix
Fixes for compiling with CUDA 6.5

Based on commit feb74b125d7923c0bc11054b66863e1e9f753141 from 2.4.9 branch.
Fixing Matx ostream operator

cv::Matx could not be converted to c::Mat automatically
Merge pull request #3177 from PhilLab:patch-3
don't use IPP on ARM
Merge pull request #3176 from ilya-lavrenov:ipp_arm
Merge pull request #3166 from akarsakov:ocl_native_sqrt
Merge pull request #3173 from rokm:cuda-6.5
Merge pull request #3170 from ElenaGvozdeva:ocl_fix