Introduce a meta_box_cb argument for register_taxonomy().

The specified callback function is used as the meta box callback for the taxonomy.

props garyc40, helen.
fixes #14206.


git-svn-id: https://develop.svn.wordpress.org/trunk@25572 602fd350-edb4-49c9-b593-d223f7449a82
Improve inline documentation of arguments for `comment_form()`.

See #25388.


git-svn-id: https://develop.svn.wordpress.org/trunk@25573 602fd350-edb4-49c9-b593-d223f7449a82