Mac windowing was further revised, and the Macintosh code was ported to
Think C by Barton House.  Amiga windowing was also touched up.

The MSDOS black/gray/white intensities were changed again to avoid
confusing displays on some PC hardware.  New video options were added
to allow configuration around any other oddities.

Bugs were fixed.  In particular, an elusive bug dealing with horns of
plenty was finally found, along with a couple VMS-specific ones such as
fetching some bones files.  A number of messages were revised and updated
as well.

Bones files and saved NetHack 3.1.2 games will not work with NetHack 3.1.3.
Delete them, to avoid problems.