Update Dashicons.

New icons: `.dashicons-external`, `.dashicons-editor-contract` and `.dashicons-universal-access-alt`.
Updated icons: `.dashicons-code`, `.dashicons-universal-access`, `.dashicons-arrow-x-alt` and `.dashicons-arrow-x-alt2`.
Restores also `.dashicons-post-trash` as an alias for `.dashicons-trash`, which is the new one.

props melchoyce, empireoflight.
see #26936.

git-svn-id: https://develop.svn.wordpress.org/trunk@27989 602fd350-edb4-49c9-b593-d223f7449a82
Avoid stomping of bulk postdata inside the bulk_edit_posts() loop.

props kovshenin.
see [27964], see #27452.


git-svn-id: https://develop.svn.wordpress.org/trunk@27990 602fd350-edb4-49c9-b593-d223f7449a82