TinyMCE:
- Fix toolbar icons in IE9.
- Remove background gradients in IE < 10.
- Lint our plugins.
- Add draggable attribute to the caption wrapper and make the captioned images non-draggable in Chrome.
See #24067.

git-svn-id: https://develop.svn.wordpress.org/trunk@26880 602fd350-edb4-49c9-b593-d223f7449a82