This gives a deprecation warning - that's kind of good, but in a developer build -Werror is on to stop warnings creeping into the code, and "expected warnings" are unhelpful as they're distracting.  So we disable deprecation warnings in the testsuite where we are testing a deprecated feature like this - look at how `api_backend.cc` defines `XAPIAN_DEPRECATED` before it includes xapian.h.