Check all statements are reset at Pool.Close

[crawshaw]

We already check Conn.CheckReset in Pool.Put. All we have to do is make sure all connections are returned to the pool before Close is called.

[FiloSottile]

I'm not sure CheckReset is checking the right thing. lastHasRow is false if the last step returned SQLITE_DONE, but I can't find anywhere in the docs a guarantee that it's the same as being reset.

For example, I wonder if the implicit transaction is committed:

An implicit transaction (a transaction that is started automatically, not a transaction started by BEGIN) is committed automatically when the last active statement finishes. A statement finishes when its prepared statement is reset or finalized.

Pool.Put should probably call Reset automatically if lastHasRow is false, though.