Skip image mime type tests if both fileinfo PHP extension and mime_content_type() function are missing.

fixes #26155.

git-svn-id: https://develop.svn.wordpress.org/trunk@26318 602fd350-edb4-49c9-b593-d223f7449a82
Restore "Skip to toolbar" link color. fixes #26146.

git-svn-id: https://develop.svn.wordpress.org/trunk@26319 602fd350-edb4-49c9-b593-d223f7449a82