sqld: disable checkpoint on primary conn create

[LucioFranco]

This commit changes our primary connection initialization code in two ways to achieve the ability to disable checkpointing the wal.

1. We ignore the initial checkpoint that we call directly into sqlite3
   before we restore from bottomless. There is a fixme above that
   explains why we need this but to me right now its not totally clear
   why without digging deeper into the internals of bottomless. We
   should do this but for the moment this unblocks us and from the fixme
   comment it does not sound unsafe rather doing extra work potentially.

2. When bottomless needs to get the local change counter is creates a
   sqlite connection. When this connection drops it seems like it
   checkpoints the wal. I took a brief look at the sqlite3_close code
   and did not find anything obvious, I have been told in the past that
   sqlite3 likes to checkpoint at weird points so this could be one of
   those. For the moment, the temporary fix like above is to
   std::mem::forget the connection so that Drop never gets called
   and thus sqlite3_close never gets called.

With both of these changes we now don't checkpoint the wal unless we hit the max size or interval (which for testing I have set very high).