[plt-scheme] 204.3

The exp-tagged code in CVS for MzScheme and MrEd is now version 204.3.

The changes are mainly cosmetic, again:

 * Windows, Mac OS: text fields look they way they're supposed to look.
   (The border and hiliting of a text field used to look wrong,
   compared to the platform's standard text-field control.)

 * Added a 'control-border style to canvas% and editor-canvas%, which
   gives the canvas a text-field-style border.

 * Added a 'hilite style for pen% and brush%. Under X, it's the same as
   'xor. Under Windows and Mac OS, it does something platform-specific
   so that the existing image looks hilited. (See the manual for
   details.)

 * Windows: the default 'system font is "Tahoma" when available ---
   normally XP and 2000 --- or "MS Sans Serif" otherwise. The default
   'default font is "Microsoft Sans Serif" when available --- normally
   XP --- or "MS Sans Serif" otherwise. ("MS Sans Serif" is a bitmap
   font, and "Microsoft Sans Serif" is an outline font.)

 * Added a 'no-autoclear style to canvas%, which suppresses an
   automatic `clear' for portions of a canvas that need to be updated.

 * OS X: key-release events are now reported.

 * Added `locked-for-write?', `locked-for-flow?', and
   `locked-for-read?' methods to editor<%> for reporting the state of
   internal locks.

Matthew