Backstory: I needed a better way to pass around information about the
underlying driver and implementation to all the various db-using things
in satellitedb (at least until some new "cockroach driver" support makes
it to DBX). After hitting a few dead ends, I decided I wanted to have a
type that could act like a *dbx.DB but which would also carry
information about the implementation, etc. Then I could pass around that
type to all the things in satellitedb that previously wanted *dbx.DB.
But then I realized that *satellitedb.DB was, essentially, exactly that
already.
One thing that might have kept *satellitedb.DB from being directly
usable was that embedding a *dbx.DB inside it would make a lot of dbx
methods publicly available on a *satellitedb.DB instance that previously
were nicely encapsulated and hidden. But after a quick look, I realized
that _nothing_ outside of satellite/satellitedb even needs to use
satellitedb.DB at all. It didn't even need to be exported, except for
some trivially-replaceable code in migrate_postgres_test.go. And once
I made it unexported, any concerns about exposing new methods on it were
entirely moot.
So I have here changed the exported *satellitedb.DB type into the
unexported *satellitedb.satelliteDB type, and I have changed all the
places here that wanted raw dbx.DB handles to use this new type instead.
Now they can just take a gander at the implementation member on it and
know all they need to know about the underlying database.
This will make it possible for some other pending code here to
differentiate between postgres and cockroach backends.
Change-Id: I27af99f8ae23b50782333da5277b553b34634edc
