Turns out, you can't use preprocessor directives inside macro arguments.
Who'd have thought?

Now it allows choosing between arbitrary implementation variants.

+ interpolateFrames and createOpticalFlowNeedleMap

Also cv::, cv::gpu:: and cv::ocl:: namespace prefixes can be safely omitted
inside CV_ENUM and CV_FLAGS

* disabled warnings from thrust
* fixed warnings from ts_gtest.h
* possibly fixed superres compilation in Debug mode on Windows

* added DenseOpticalFlow interface
* moved OpticalFlowDual_TVL1 to src folder