I1620 : Changes from Bob Supnik re: Bob Armstrong has been running diagnostics and software, and these changes reflect fixes to bugs that were found.

We're not absolutely sure that all of the changes are correct - in particular the treatment of record marks in add/compare - but they do make the diagnostics pass, which they didn't before.

Bob asked for variable tab stops on the typewriter, and those are implemented as well. The routines were general enough that I put the SET/SHOW processors in sim_console.c, so I'm enclosing that and its header file.

Conflicts:
	I1620/i1620_cpu.c
	sim_console.c
	sim_console.h