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.
