Image post format UI:
- When initializing wp.Uploader pass null for 'container' and 'browser'. Fixes a bug where another instance of the uploader was attached to <body>.
- Destroy the uploader instance if drag/drop is not supported (IE8 & 9).
See #24291.

git-svn-id: https://core.svn.wordpress.org/trunk@24310 1a063a9b-81f0-0310-95a4-ce76da25c4cd