Plugin Installer: Disable 'Latest Version Installed' buttons.

props paulwilde.
see #26952.


git-svn-id: https://develop.svn.wordpress.org/trunk@27677 602fd350-edb4-49c9-b593-d223f7449a82
Ensure Thickbox loading spinner is properly sized for HiDPI displays.

props paulwilde.
see #26952.


git-svn-id: https://develop.svn.wordpress.org/trunk@27678 602fd350-edb4-49c9-b593-d223f7449a82