Bumping the MI level

[Nick Roberts]

I think we should collect together all th incompatible changes that we
would like to make to MI and, perhaps after the next release, bump the MI
level up one.

Here's a change I would like to make for the new level (it partly relates to a
thread from a few years ago):

    All user errors in MI to go through error () and get caught by
    mi_execute_command.

    All MI errors, e.g, "mi_cmd_thread_select: USAGE: threadnum." to go
    via MI_CMD_ERROR/mi_error_message back to captured_mi_execute_command
    and use a new RESULT-CLASS, ^internal-error, say.  These are errors
    that should only occur if the front-end is improperly configured.

-- 
Nick                                           http://www.inet.net.nz/~nickrob