Display PlusCal translator warnings in the toolbox interface

[ztlpn]

This PR is in preparation for #624

Currently PCal translator doesn't emit many warnings (namely two: "symbols were renamed" and a warning about conflicting fairness options if --fair algorithm has been specified) but I think it still makes sense to display them (and possible future warnings) in the toolbox interface.

This also fixes a small bug where PCal warning messages didn't get their own message in ToolIO and instead got coalesced the next message.

[ztlpn]

Re: #624 (comment)

By "the new warning" do you mean the warning about the dangling blocks or the warning about conflicting fairness options? The latter one isn't new :) anyway it is triggered by

------------------------------ MODULE warning ------------------------------

(*
PlusCal options (-nof)

--fair algorithm test
variables x = FALSE;
begin
    x := TRUE;
end algorithm;
*)

=============================================================================

If you wish, I can add it to test cases – at the very least it would test that warnings are properly registered in ToolIO.

Also there is a warning generated when identical labels in different processes are renamed. Which is a bit superfluous in my opinion - info about label renames also is written into the translation header. But I can leave it as-is.

As far as I can see, there are no other warnings in the existing code.

[lemmy]

Yes, please add the test you're proposing. I've always found the warning at the translation header sufficient. Perhaps, create a new issue once the current one is addressed?

[lemmy]

I'm not sure we should roll this change into this PR for backward compatibility reasons. Is there a reason for removal besides it being annoying?

[ztlpn]

No other reason. I'll revert it then.