Add a short Ogg Opus file to the content/media/test
directory and add it to the gSeekTests, gSmallTests,
and gPlayTests in manifest.js. This file is crafted
to end on a packet boundary, so trimming to duration
is not verified.
Set the media.opus.enabled pref to true in manifest.js
so the various tests using the opus file succeed.
Add a stanza to can_play_type_ogg.js to test the
behaviour of canPlayType with an opus-specific
media type for both values of the pref.
Add support for the .opus filename extension to
the mochitest http server.
