bug#5122: Mismatched parentheses when dealing with huge buffercontent

[Chong Yidong]

> I think it's better to modify the echo area message, such that if
> Emacs hits the blink-matching-paren-distance limit (as opposed to
> hitting point-min), the message says something like
>
>   Mismatched parentheses (within blink-matching-paren-distance)

Error messages shouldn't be so verbose---they can't spell out every bell
and whistle related to the error.  I prefer leaving things the way they
are.