[xslt-conformance] Notes about cataloging

[David Marston/Cambridge/IBM <david_marston@us.ibm.com>]

I was just scanning our test group named "variable", since that is one
of the groups we wanted to get into soon. I noticed that we have some
tests that involve imported/included stylesheets, so the phase where
there are more than two inputs is already upon us. Of course, the
catalog design makes provision for this, so I'm just pointing it out as
a reminder that not all the cases will be the simplest scenario.
.................David Marston