fixed kernel compilation in imgproc module
eliminated warning C4267
Merge pull request #1848 from ilya-lavrenov:warn
Merge pull request #1847 from ilya-lavrenov:ocl_imgproc_fix
changed eps in Retina_OCL test
Merge pull request #1852 from ilya-lavrenov:ocl_retina
ocl/core: added prototype for tests