Customizer: Only tie header button action events to the header controls.

Merges [28269] to the 3.9 branch.

props danielbachhuber.
fixes #28046. see #27848.


git-svn-id: https://develop.svn.wordpress.org/branches/3.9@28270 602fd350-edb4-49c9-b593-d223f7449a82