Escape late in get_avatar().

Merges [29397] to the 3.9 branch.

Built from https://develop.svn.wordpress.org/branches/3.9@29398


git-svn-id: http://core.svn.wordpress.org/branches/3.9@29176 1a063a9b-81f0-0310-95a4-ce76da25c4cd