Add the AddCharset functionality to mod_mime.

Submitted by:	Youichirou Koga <y-koga@isoternet.org>
Reviewed by:	Ken Coar, Martin Kraemer


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@84265 13f79535-47bb-0310-9956-ffa450edef68