Merge commit '303fadf5'

* commit '303fadf5':
  avconv: Document the -init_hw_device option
  avconv: Enable generic hwaccel support for VDPAU
  lavc: vdpau: add support for new hw_frames_ctx and hw_device_ctx API
  lavc: Add hwaccel_flags field to AVCodecContext
  avconv: Enable generic hwaccel support for VAAPI
  avconv: Generic device setup
  hwcontext: Make it easier to work with device types
  hwcontext: Add device derivation

This commit is a noop, see
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527a1e21Merged-by: James Almer <jamrial@gmail.com>