a crash with the libv4l capture code

Rectified this, hopefully.

extended Python bindings; not merged into cv.cpp yet; and many of the helper functions, like pyopencv_to_*, pyopencv_from_* etc. are still missing

extended Python bindings; not merged into cv.cpp yet; and many of the helper functions, like pyopencv_to_*, pyopencv_from_* etc. are still missing

modified features2d interface; added algorithmic test for DescriptorMatcher; added sample on matching to many images

added more helper macros to the function declarations, to assist the Python wrapper generator. Fixed memleak in Mat::operator()(Range,Range) and the related functions (Mat::row, Mat::col etc.)

opencv/modules/ml/src/gbt.cpp