Introducing API limit for number of relation members

(This is cross-posted from the dev mailing list, so please see for followups there too).

We will soon be introducing an API limit to the number of members of a relation. This is due to a few problems over the years when relations
are created with huge numbers of members. The limit will be set at 32,000 members in a relation, and so it’s designed to prevent errors
getting into the database, rather than to interfere with any regular mapping techniques.

More information can be found in:

Developers of editing software are recommended to use the /api/0.6/capabilities call to retrieve the limit, in the same way that
the existing waynodes limit is published. For consistency, the error message returned is in the same format as the waynodes error message too.

If you are deploying the openstreetmap-website source code in other situations (e.g. you are using the openstreetmap-website codebase for
other projects, or for internal use) please note that the limit can be adjusted in the configuration files, as usual.