Better sanity checks in oEmbed XML handling.

Merges [24470] to the 3.5 branch.



git-svn-id: http://core.svn.wordpress.org/branches/3.5@24471 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Build the media item HTML in a clearer manner in the legacy Plupload handler JS. Also update the retired SWFUpload handler JS.

Merges [24472] to the 3.5 branch.



git-svn-id: http://core.svn.wordpress.org/branches/3.5@24473 1a063a9b-81f0-0310-95a4-ce76da25c4cd