[plt-scheme] 299.27

The exp-tagged code in CVS for MzScheme and MrEd is now version 299.27.

Changes:

 * Changed gl-context% `swap-buffers' to use the `call-as-current' lock,
   and changed the lock to be re-entrant.

 * Added gl-config%, which encapsulates configuration information for
   an OpenGL context (e.g., size of the stencil buffer, size for
   multisamples).

   A gl-config% object can be used as an initialization argument to
   canvas% or as the argument to bitmap%'s `set-gl-config' method.

 * Keyboard navigation now includes tab-panel controls.

 * Mac OS X: full keyboard access is now supported. (Enable full
   keyboard access through the "Keyword" panels of system preferences.)


Matthew