Final about page.

props melchoyce, helen, wonderboymusic, nacin, and the illustrious Michael Pick.
fixes #27713, #27837.

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About page: Don't use wp_playlist_scripts() as that prints stuff.

fixes #27713.

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Prevent customizer header image list from listing user images twice when no theme-specified images exist

fixes #27839. props mcsf
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WordPress 3.9.

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