Log Message:
Update lang/drscheme to current version 202.

Changes since our last version (103) include (but obviously
are not limited to):

New Homepage http://www.drscheme.org

  drscheme:
    - removed 'project manager' (use 'module' instead)
    - added profiling support
    - support for different natural languages
    - added module browser
    - added XML boxes
    - new menu-items
    - improved error message output
    - added an emacs-like c-x c-b feature
    - improved documentation
    - teachpacks support macro definitions
    - now prints exact real numbers as graphical fractions
    - misc bug fixes
    - improved create executable interface
    - improved interaction between help desk and external browser

  mred:
    - many new key- and mouse events
    - various changes (additions and removals) of different methods
    - Added 'unknown/mask and 'unknown/gif bitmap types
    - New load handler, text-editor-load-handler

  mzscheme:
    - new module system
    -  No object or unit system is built into MzScheme.
    - The core syntax system is hygienic;
    - Modules can replace units where units are used merely for namespace
      control
    - The `struct' form is gone, replaced by a more flexible
      `make-struct-type' form
    - various process procedures have been moved to a new
      MzLib library, "process.ss"
    - The built-in regular-expression matcher works on input ports
    - The mzc compiler supports a subset of the Gambit-C foreign-function
      interface

  teachpack:
    - Fixed bug in convert.ss
    - removed: pingp-play.ss pingp.ss protect-play.ss rectangle.ss
    - all exported functions are primitive operators or higher order primitives
      this improves error reporting behavior in the Beginner languages
    - added servlet.ss and servlet2.ss

  stepper:
    - Total rewrite for new syntax. Addition of test suites.
    Addition of somewhat more systematic macro unwinding.
    Lots of bug fixes.