[plt-scheme] 204.2

The exp-tagged code in CVS for MzScheme and MrEd is now version 204.2.

Changes:

 * Added a 'toolbar-button style to frame%, and an
   `on-toolbar-button-click' method, which are useful only under Mac OS
   X. The 'toolbar-button style adds a toolbar button (a little oval on
   the right) to the frame's title bar under OS X. The method is called
   when the toolbar button is clicked.

 * Added a `modified' parameter-like method to frame%. Under OS X, a
   "modified" frame's close button displays a dot inside. Under
   Windows, a "modified" frame's title has an asterisk appended.

 * Changed menu-bar% so that 'root can be supplied as the parent, but
   only when the new `current-eventspace-has-menu-root?' procedure
   returns #t, and only when no such menu bar has been created before.

   A 'root menu bar becomes active when no frames are shown. Also a
   'root menu bar prevents the corresponding eventspace from
   unblocking, which roughly implies that an application with a 'root
   menu bar doesn't exit when the last frame is closed.

   The `current-eventspace-has-menu-root?' procedure returns #t only
   for the main eventspace and only under Mac OS (X and Classic).

 * Added `super-new' to go with `new' in (lib "class.ss").

Matthew