Update to 0.5.1. Depend on devel/waf. Install configuration file
using pkgsrc config file framework.

Changes:

    Add audio/flac to the MIME type list in mpv.desktop.
    The --slave-broken option has been reintroduced and is equivalent
    to using --input-file=/dev/stdin and --input-terminal=no.

Bug fixes

    Fix screenshots with anamorphic videos in the vdpau vo.
    Fix a crash happening when mpv fails to create a vdpau mixer
    in the vdpau vo.
    Don't quit when the --loop-file option is used.
    Always load the cursor theme in the wayland vo (this fixes a
    crash caused by moving the mouse cursor over the video).
    Properly return non-zero from the zsh completion script when
    no matches are found (this fixes the use of user-defined zsh
    completion matchers).
    Fix the description of the opengl-hq vo default options in the
    manpage.
    Remove duplicated content from the manpage that was accidentally
    added in the manpage reorganization from the previous release.
    Avoid clobbering playback position on video end (when both
    audio and video streams reached the end, the playback poisition
    was briefly set at 0).
    Avoid overwriting user input in the coreaudio_device ao.
Remove mpv, imported to multimedia/mpv.