For several muxers and encoders GStreamer still drops the last frame.

- Accurate ASYC task handling for both GStreamer generations.
- Correct video duration request for videos.
- More accurate pipeline destruction.
- Correct color space conversion plugin for GStreamer 1.0.

underline

sss

Added workaround for Nvidia: take into account that 3-channel vector type takes 4*elem_size in local memory.

don't discard pure virtual methods in hdr_parser.py (was broken anyway)

cv::Matx could not be converted to c::Mat automatically

As opencv_xfeatures2d is part of opencv-contrib and not opencv repository,
${OpenCV_SOURCE_DIR}/modules/modules/include is not a correct include
path - use ${opencv_xfeatures2d_SOURCE_DIR}/include instead

The cv::superres::createOptFlow_Simple() function along with the
simple optical flow class implementation is currently commented out
in the superres module's code, so comment it out in the example as well.