[m-rev.] for review: fix two bugs in the management of I/O tabling

[Zoltan Somogyi]

On 26-Sep-2007, Ian MacLarty <maclarty at csse.unimelb.edu.au> wrote:
> I think the problem here is that the standard library is trusted by
> default, so the declarative debugger will never ask any questions about
> io.read

Yes, I know.

> Perhaps the fix is to never trust the initial node, and always require
> an answer from the user for the initial node?

No, that won't fix the underlying problem, which is that climbing out of the 
original tree is *possible at all*.

> Perhaps the solution is to document this behaviour more clearly.

This doesn't work:

	"You cannot make a pussycat out of a lion
	by describing its claws in a reference manual."

I am pretty sure the fix has to involve the code I marked in
declarative_tree.m, but we probably need to get some extra information
(the call sequence number of the call being debugged, or the event number
of its call event) to that code so it can do its job correctly.

Will you come in tomorrow or friday?

Zoltan.
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