made FLANN (and dependent on it code) build fine on Windows. Most of the changes are added CV_EXPORTS' into the class declarations and extern variables are turned into external functions (as a nice side effect the variables are now read-only)

Gradient Boosting Trees (CvGBTrees) added to opencv mll. Test for all CvGBTrees public methods added.

added supports of CV_32SC2 source to gpu scalar arithm and float source to gpu::histRange.
minor fix of gpu tests.

added supports of 4-channels image to gpu::minMax and gpu::cvtColor for RGB <-> YCrCB, RGB <-> YUV and RGB <-> XYZ color conversion.

disabled gpu::sum, gpu::minMax, gpu:Canny until fix crash.