As a prerequisite for cleaning up some other include issues, all the
include files in inc/ should have an include guard. All the xxxdefs.h
were created with them, but most older files were not.
This also removes support for the DEC3100 keyboard, but leaves a
constant behind for it as I'm not sure about re-numbering.
[NBriggs: keyboard type numbers are stored within all sysouts. Do not renumber supported keyboards, do not reuse previously used keyboard numbers]
This platform had no emulation-related changes.
Remove code for IRIX40, INDIGO definitions.
In disk code, simplify a chain of #ifdef's around fsync handling.
Ultrix hasn't seen an update since 1995 and the DEC3100 hardware
that this was originally written for was released in 1989.
It isn't likely that anyone has Ultrix running on hardware where
they would also want to run this.
