Properly account for text overflow in .wp-playlist-caption by adding display: block.

Merges [28172] to the 3.9 branch.

props celloexpressions.
see #27923.

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Add calc() rules for max-width of playlist caption.

Merges [28174] to the 3.9 branch.

props celloexpressions.
fixes #27923.

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Don't set the poster image for videos in a playlist if the image is the video mime-type icon blown up.

Merges [28158] to the 3.9 branch.

props wonderboymusic.
see #27892.

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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.

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