The method ocl::oclMat::ptr() is being removed because it returns a pointer to a row of oclMat::data. The data attribute is a cl_mem structure and cannot be iterated outside an OpenCL kernel.

minor improvements

The oclMat::ptr() method was mistakenly used in ocl::BruteForceMatcher to pass a pointer to a oclMat object. The ptr() method returns a uchar pointer to the cl_mem data structure and this method will be removed.

There are some mixed implicitly/explicitly type conversion between
scalar and vector. Although the spec allows those conversion, I prefer
to make them consistent and use explicitly all the cases.
Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>

_MSC_VER -> defined _MSC_VER. Fixes building with MinGW.
Similar to fbc91c5e.

check that input images was loaded correctly