The ingest API tried to do a Qcx operation that needs a write Tx after
requesting a write Tx. This doesn't work. The ingest API is the only caller
of clearExistenceColumns, so it's easy to just make it work for a given
shard using a provided Tx. This isn't especially clean, but a lot of this
is due for an overhaul anyway because the Qcx/Tx stuff is sort of broken.
Also, add any test case at all for this, since we didn't have one, and
also fix the fact that the test case failed because the test harness
didn't allow empty result sets.
This is a design to let us write test cases for ingest with schema setup
and data in the json formats we want to use, and results as alternating
queries and expected results, so we can just create new test files and
run the tests against them. We also have to report back what we created
when creating things.
In the process of developing this, I noticed that the documentation describes
ingest schema as allowing more than one schema operation, but we didn't support
this, and also it wouldn't do much good because there was no way to do partial
things like "just add a field". Fixed.
Also we implement comparison for ops, so the test output is actually
a test rather than just some data to visually eyeball.
In the process, realize that the handling of timestamps was wrong; we said that we
take them as raw numbers relative to the epoch, not as raw Unix timestamps.
Also a couple of related cleanups caught by doing the testing.
