Add a compatibility layer in wp-playlist.js to avoid VM errors from MediaElement's plugin bridge in the TinyMCE views for playlists by suppressing playback for files whose mime-type is not supported in the user's browser natively.

Merges [28171] to the 3.9 branch.

props wonderboymusic.
fixes #27892.


git-svn-id: https://develop.svn.wordpress.org/branches/3.9@28247 602fd350-edb4-49c9-b593-d223f7449a82