on-reorder (augmentable only) in pasteboard%

Called before a snip is moved in the pasteboard's front-to-back snip order, after can-reorder? is called to verify that the reorder is allowed. The after-reorder method is guaranteed to be called after the reorder has completed.

The editor is internally locked for writing when this method is called (see also Locks). Use after-reorder to modify the editor, if necessary.

• (send a-pasteboard on-reorder snip to-snip before?) -> boolean
     snip : snip% object
     to-snip : snip% object
     before? : boolean

  If before? is #t, then snip is to be moved before to-snip, otherwise snip is to be moved after to-snip