bug#24861: [PATCH] Fix annoying "Parsing...done" message in c++-mode

[Eli Zaretskii]

> From: Hong Xu <hong@topbug.net>
> Date: Wed, 02 Nov 2016 13:09:15 -0700
> 
> +(defcustom cpp-message-min-time-interval 1
> +  "The minimum time interval in seconds that cpp-mode should
> +print messages.  No message will be printed if set to
> +`most-positive-fixnum'."

Please avoid using passive tense as much as possible (in the last
sentence).

Also, I think it's accepted practice to use nil as the value which
disables a periodic feature.

(Not that I understand why this particular message needs to be
customizable.)

Thanks.