* Reorganize the PM interface to encapsulate PM event messages and send

* Reorganize the PM interface to encapsulate PM event messages and send
  them to the window's event qid in their original format.  This
  simplifies the process of adding new event types, and allows the
  window's owner to decide what is relevant information.

* Add some new interface calls to support mouse tracking and pop-up
  menus.

* Implement a mechanism to mark characters with the mouse in the
  console window, and a Copy command to copy them to the clipboard.