In the admin, give media list table icons `auto` for `width` and `height`. In the post thumbnail metabox, apply `width: auto`. 

If someone turns on support SVG files, this will allow them to show up.

Props arippberger for an initial patch.
Fixes #26256.

Built from https://develop.svn.wordpress.org/trunk@29832


git-svn-id: http://core.svn.wordpress.org/trunk@29596 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Allow PSDs (Photoshop documents) to be uploaded.

Props michalzuber, ccprice.
Fixes #28805.

Built from https://develop.svn.wordpress.org/trunk@29833


git-svn-id: http://core.svn.wordpress.org/trunk@29597 1a063a9b-81f0-0310-95a4-ce76da25c4cd