A line containing the matched open parenthesis will be displayed in
the echo area if that parenthesis is offscreen when the user types a
close parenthesis.

However, for example, the matched line may contain so many parentheses

```
(... (... ((((((((
...
...
```

that user will be confused by the text displayed in the echo area:

```
(... (... (((((
```

This patch changed a Lisp function `blink-matching-open' and rewrote a
Lisp function `blink-paren-open-paren-line-string' in order to help
user recognize the matched parenthesis more easily.

--
shynur