Fixed bug where dropChannel broadcast wrongly on hover.

- When unit testing the code I noticed that when setting
  dropChannel to '*' there would be situations where
  the regex compile in isDragChannelAccepted() would
  fail.  The onDragEnter() handler is broadcasting the
  dropChannel, and the handler for the ANGULAR_HOVER
  event is receiving it and passing it to
  isDragChannelAccepted() as the drag channel.  Changed
  so that onDragEnter() sends the drag channel instead.