Re: (ITS#5810) $BACKEND selections in make test

[h.b.furuseth@usit.uio.no]

All tests now check for backends they do _not_ support, not for
which ones they do support.  They note why backends get exluded.

./run -b ndb all" accordingly runs the following tests which it didn't
before.  If any of that was intentional, ndb needs to be re-excluded.
	test006-acls
	test018-syncreplication-persist
	test019-syncreplication-cascade
	test023-refint
	test033-glue-syncrepl
	test040-subtree-rename
	test041-aci
	test043-delta-syncrepl
	test045-syncreplication-proxied
	test054-syncreplication-parallel-load
	test055-valregex
	test057-memberof-refint
	test058-syncrepl-asymmetric

Beyond that, I seem to have confused this ITS with an "add support
for back-ldif and back-null" ITS, so I'll continue that way.

back-ldif passes the tests I can run here.  back-null now fails 6
tests.  Need to look closer to figure out if any failures are bugs
(or doc bugs), which is kind of the point of the exercise.

-- 
Hallvard