blink-matching-open resizes echo area

[martin rudalics <rudalics@gmx.at>]

Suppose all "blink-matching..." variables at their standard settings.
When I now insert a closing paren in the current buffer and (a) the
matching paren is before `window-start' and (b) the `buffer-substring'
to be displayed by `blink-matching-open' contains at least one bold
character, the following happens: Emacs resizes the echo area to show
the string (apparently to accomodate the bold character) and recenters
the current buffer.  The combined effects are distracting.

A workaround is to replace `buffer-string' in `blink-matching-open' by
`buffer-substring-no-properties'.  Binding `max-mini-window-height'
temporarily to 1 is better - Emacs doesn't recenter any more but still
resizes the echo area.  Personally, I'd prefer a solution that would not
resize the echo area at all in this particular case but probably I'm
asking too much.

An aside: When I activate `show-paren-mode' the latter setqs the
variable `blink-matching-paren-on-screen'.  Customizing that variable
now tells me "CHANGED outside Customize; operating on it here may be
unreliable".