Fix Doxygen mark-up.

* subversion/include/svn_auth.h
  (svn_auth_cleanup_callback): Fix mark-up and a parameter name.

* subversion/include/svn_client.h
  (svn_proplist_receiver2_t, svn_client_propget5): Fix mark-up.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1444974 13f79535-47bb-0310-9956-ffa450edef68