Add HammingDist test case
Untabify
Pass query type T into kernel
Enable runtime type definition in kernels
Allow more input query/train types for ocl::bfmatcher

RadiusMatch for HammingDist cannot pass yet.
Allow more query/train types for ocl::bfmatcher
Merge branch '2.4_ocl_bfmatcher_newtype' of https://github.com/pengx17/opencv into 2.4_ocl_bfmatcher_newtype
Use a faster way to count 1's (used by Hamming)
Update gtest to upstream r652

It is already marked as a gtest 1.7.0
Fix build issues
Merge pull request #811 from pengx17:2.4_ocl_bfmatcher_newtype
Merge pull request #814 from taka-no-me:gtest_r652
Add contributing page for Github
Merge pull request #821 from taka-no-me:contributing