Fix a regression in wp_mkdir_p() where the $mode of the parent folder is not correctly applied to all created paths.

Merges [26449] and [26927] from 3.8.x to the 3.7 branch.

props dd32.
fixes #25822.

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git-svn-id: http://core.svn.wordpress.org/branches/3.7@27718 1a063a9b-81f0-0310-95a4-ce76da25c4cd