Detect and handle symlinking of plugins in plugin_basename().

props rmccue, MikeSchinkel, jdgrimes.
see #16953.

Built from https://develop.svn.wordpress.org/trunk@27158


git-svn-id: http://core.svn.wordpress.org/trunk@27024 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Edit image in TinyMCE:
- Add a "toolbar" at the top of the image with two buttons: Edit and Delete.
- Don't open the edit modal on second click on the image. Makes the "edit" button somewhat pointless and can sometimes trigger after resizing the image.
- When the image has caption: attempt to prevent IE11 from making the caption element resizable and wrapping it in thick border.
- When the caret is inside a caption next to the image, pressing Enter will create a new <p> tag above the caption.
- Hide the image toolbar on drag, cut, align.
Props gcorne, see #24409.
Built from https://develop.svn.wordpress.org/trunk@27159


git-svn-id: http://core.svn.wordpress.org/trunk@27025 1a063a9b-81f0-0310-95a4-ce76da25c4cd