Fix the exclude_tree argument in get_terms(), which fixes the exclude argument in wp_list_categories().

Merges [25933] to the 3.7 branch.

This was a 3.7 regression caused by [25162].

props dd32.
fixes #25710.


git-svn-id: https://develop.svn.wordpress.org/branches/3.7@25936 602fd350-edb4-49c9-b593-d223f7449a82