Error printing, and "silent" BREAK loops

[JONL at MIT-MC (Jon L White)]

    Date: 12 July 1980 16:23-EDT
    From: Kent M. Pitman <KMP at MIT-MC>
    I propose that if MSGFILES is () that the error be forced to the terminal
    if Lisp wants to do that, but if MSGFILES is non-(), it should only go to
    there. That will let us create an SFA to gobble all error messages and 
    behave appropriately. -kmp
Sounds good - I've just made that patch.  I believe that there is only one
place, in ERRPRINT, where the "inhibit-forcing-the-TTY" bit is set, relevant
to this problem.