fix gpu warnings with signed/unsigned char
optimize hog
revise accuracy and perf tests
revise ocl samples, add tvl1 sample
Make version-related test properties more useful.

Namely, normalize their names to a common convention and remove useless text
from their values.
Give cv::ocl::CLAHE a virtual destructor, for the usual reasons.
Fix a bug of convertTo.
The bug was found that all 3-channel oclMat's were converted to
4-channel oclMat's after using convertTo function.
Merge pull request #1017 from jet47:fix-gpu-warnings
A few minor improvements to the XLS report generator.

* In comparison column headers, switched the order of labels, so that
  it's "to" vs "from".

* When a test was present, but not run successfully, put its status in
  the corresponding cell instead of coloring it gray.
Use log formatting as intended.
Add a workaround to interpolate between oclMat and Input/OutputArray.
a bug fix in stereo_match sample
Revise naming for getOclMat function.
Merge pull request #1033 from SpecLad:xls++
Merge pull request #1026 from SpecLad:ts-version-prop
Merge pull request #1022 from bitwangyaoyao:2.4_hog
Merge pull request #1025 from bitwangyaoyao:2.4_tests
Merge pull request #1031 from pengx17:2.4_fix_converTo
Merge pull request #1034 from pengx17:2.4_oclmat_inoutarray
Merge pull request #1028 from SpecLad:ocl-clahe-dtor