Trac has support for what are called inter-trac links
http://trac.edgewall.org/wiki/InterTrac

They are useful because they allow for cross-referencing between two different
Trac systems.

We have two different trac systems in use, one for standard bug tracking use,
and one we use for tracking changes (including software rolls) to our production
environment. This means that our changelists have tokens like
trac:ticket:113 and
production:ticket:241

With InterTrac configuration, Trac resolves these into links to the correct trac
installation. However, the Hudson Trac plugin doesn't recognize these intertrac
style links and instead would create (for the example above) a link to ticket
113 in the trac system and a link to ticket 241 in the trac system.

It would be helpful if the Trac configuration for a Hudson job would also
support Inter-trac style links.