MI testsuite improvements

[Andrew Cagney]

Bob Rossi wrote:
> Hi,
> 
> This patch is a prerequisite to the patch that includes the syntax
> checker for the MI output commands.

> It does several things,

Please, one change, one patch.

>    - Gives the inferior it's own PTY to send output to

I'm ok with this, as I think you noted elsewhere, this has become the 
defacto standard.  Would you be interested in documenting this?

The change should be applied to just mi-* and not mi2-*, and should only 
accept plain text on that PTY.   @... output on the PTY should be 
rejected ("in theory" so should anything on GDB's pty).

Once you've committed this, we can look at the next problem.

Andrew