bug#11212: 24.0.95; mailcap-mime-extensions: Add opendocument formats

[Glenn Morris]

Eli Zaretskii wrote:

> This file seems to come from mime-support, which is a Debian package.
> Do other Posix systems, whether other GNU/Linux or Unix, also have
> this file?

I'm 99% sure all halfway modern GNU/Linux systems have such files.
Eg, Red Hat based ones do. Less sure about any other Unix.
mailcap-poor-system-types suggests they do.

> OTOH, if we want to rely on this file, then why do we have a non-empty
> mailcap-mime-extensions at all?  And why adding a few more entries to
> that list should be rejected?

I'm not rejecting anything; but since this issue mainly affects MS
Windows it's not a high priority for me personally to change it.

mailcap-mime-extensions is weird (IMO), in that there is a default
(which is a defcustom) that gets modified behind the user's back. It
would be cleaner to separate it out into different variables.
An empty one for the user's customizations, one that gets the system
entries added to it, and a fallback one for systems without databases.
I think it's fine to add many more entries to the last one.
Or stick a mime-types file in the Emacs etc directory if that is easier.