Fixed problem with compilation without HAVE_OPENCL

When compiling without OpenCL, some classes from its namespace are still used in code.
Fixed trailing whitespace
Fixed error in case corners not found
fixing OCL run condition (build program failure for comparison 64F Mat with Scalar)
Merge pull request #2556 from DeanF:master
Merge pull request #2567 from apavlenko:fix_compare_scalar
Merge pull request #2562 from akarsakov:gftt_fix