be more honest about test suite failures due to old libraries

[Daniel Kahn Gillmor]

We have several places where tests are skipped or marked as though
some test suite prereqs are missing, but in fact are due to building
against older versions of libraries that don't support certain
features.

This series tries to be more honest about some of those tests by
marking them as broken, rather than just skipping them.

The series still doesn't address T650-regexp-query.sh, which is
basically entirely skipped if Xapian doesn't have a field processor,
rather than marked as broken.  But it's still an improvement in
overall test suite honesty over the status quo.