[plt-scheme] 299.21

The exp-tagged code in CVS for MzScheme and MrEd is now version 299.21.

Changes:

 * Added reader support for "#<<" here strings (compatible with Scsh).


 * X: The clipboard is now supported properly, including the
   distinction between the clipboard and the selection.

   To get the old behavior, set the 'MrEd:selectionAsClipboard
   preference in "plt-prefs.ss" to #t.

   The new MrEd object `the-x-selection-clipboard' represents the X
   selection, whereas `the-clipboard' now represents the X clipboard.

 * Added `paste-x-selection' and `do-paste-x-selection' methods to
   editor<%>.

 * Added "paste-x-selection" keymap function to those inserted by
   `add-editor-keymap-functions'.

   Changed the "middlebutton" mapping in the default text keymap
   initializer's map to use `paste-x-selection'.


 * Added 'auto-vscroll and 'auto-hscroll styles to editor-canvas%. The
   'auto-vscroll style causes the vertical scrollbar to stay hidden
   until an editor becomes long enough to need scrolling. Similarly,
   'auto-hscroll hides the horizontal scrollbar until an editor becomes
   too wide for the canvas.

   Under Mac OS, when an editor canvas stretches to its frame's
   lower-right corner, there's a potential collision with the resize
   tab. The new 'resize-corner style indicates that when only one
   scroll is visible, the remaining scrollbar should leave room for the
   resize tab. More generally, the new `set-resize-corner' method of
   editor-canvas% can be used to enable or disable this behavior
   dynamically.

 * Added `show-scrollbars' method to canvas%.

   The horizontal scrollbar can be shown for a canvas only if the
   canvas was created with the 'hscroll style; ditto for the vertical
   scrollbar and the 'vscroll style. This constraint allows the minimum
   size of a canvas to be small if it will never have scrollbars.

   The 'resize-corner style and `set-resize-corner' method of canvas%
   are the same as for editor-canvas%.


 * Added 'blank as a built-in cursor%, and implemented several standard
   cursors that were missing for Mac OS.


 * Mac OS: faster text drawing (mostly corrects the slow down
   introduced in v299.19).


Matthew