Add a class for get_comment_author_link() in Recent Comments widget.

props DrewAPicture, dannydehaan, 5um17.
fixes #27944.
Built from https://develop.svn.wordpress.org/trunk@29241


git-svn-id: http://core.svn.wordpress.org/trunk@29025 1a063a9b-81f0-0310-95a4-ce76da25c4cd