200alpha10

[Matthew Flatt <mflatt@cs.utah.edu>]

The exp-tagged code in CVS for MzScheme and MrEd is now version
200alpha10.

Significant changes:

 * The `draw-bitmap' method of a drawing context now accepts an
   optional mask bitmap.

 * Key-release events are reported via `on-char', etc.

   When a key-event% object represents a key-release event,
   `get-key-code' returns 'release, and `get-key-release-code' returns
   the released key. (Not the most elegant design, but it's
   backward-compatible, and few programs use key-release events,
   anyway.)

Matthew