bug#21953: Eliminate warnings in the emacs-25 release branch

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Thu, 19 Nov 2015 19:34:07 +0100
> Cc: John Wiegley <jwiegley@gmail.com>, dgutov@yandex.ru, Richard Stallman 
> <rms@gnu.org>, 
>       21953@debbugs.gnu.org
> 
> Even so, I get 322 cases of "initialization discards 'const' qualifier from
> pointer target type", and leaving these aside, also this (# of warns, warning
> message)

Feel free to fix those, and thanks.