[m-dev.] for review: new debugger command set (part 1 of 4)

[Zoltan Somogyi]

> And that at long last completes this round of reviewing for me.
> I'd like to see a relative diff next time.  

Most of the diff is dull, so I won't include it here; it is in the file
DIRDIFF in ~zs/mer/ws5 on hydra.

> Please be careful to ensure that all the points raised in the reviews
> are addressed -- this is a big set of changes, and so it would be easy
> for some issues to simply get lost.  I want to be sure that doesn't happen.

I addressed all the points raised, except those which I pointed out as
being based on incorrect assumptions, and the following, which are left
for future work:

maybe(int) in trace.m
generic error message function in mercury_trace_internal.c
consider adding new option type for trace options
get the debugger to talk to a different stream, not stdout
get mercury_stack_layout.h and mercury_stack_trace.c support
	the proc layout of compiler-generated procedures
make the search for the .mdbrc file more portable

Zoltan.