OpenCL SURF implementation is unstable

Incorrect "total" buffer size calculated in StdMatAllocator::allocate() due wrong step values.

clarify some passages, fix grammar errors

MacOSX OpenCL compiler is very strict to whitespace issues

To prevent unnecessary compiler invocations

CMAKE_COMPILER_ID => CMAKE_CXX_COMPILER_ID

getViewerPose() doesn't modify an object of the class so it can be
made const. It also makes this method consistent with other getters
in the class as they are defined as const.