102/13

[Matthew Flatt <mflatt@cs.utah.edu>]

The currently exp-tagged MzScheme and MrEd sources are now version
102/13, a minor improvement over 102/12. The primary reason for this
intermediate release is to test re-arranged code (see the last bullet
below) as much as possible before the release of 102.

Changes:

 * Changed `find-executable-path' to accept #f as its second argument,
   and fixed the documentation.

 * Unix: Fixed 'truncate/replace flag to `open-output-file' et al.
   (Bug introduced in 102/10.)

 * Windows: `normal-case-path' removes trailing spaces from a filename
   (because the Windows API does).

 * Windows: MzScheme recognizes special filenames like "LPT1" as
   "files" that might block on I/O (except "NUL", which never
   blocks). The `file-exists?' primitive reports #t for all of these
   "files", which can be prefixed with any path - even a non-existent
   one - and/or postfixed with any file extension or with a single
   colon!!!

 * Inside MzScheme: scheme_basic_env(), if called more than once,
   resets all threads, parameters, ports, namespaces, and
   finalizations. (Useful to MzCOM.)

 * Code maintenance: split some source files, adding builtin.c,
   network.c, numarith.c, numcomp.c, numstr.c, objclass.c, portfun.c,
   and unitsig.c.

Matthew