go/zodb: Connection -= .stor

Connection has .db and db has .stor - there is no need to keep separate
.stor on the Connection. This thinko was there from Connection beginning
(533f0c73 "go/zodb: DB - application-level handle to database (very draft)")

go/zodb/connection.go

@@ -45,7 +45,6 @@ import (
 //
 // Use DB.Open to open a connection.
 type Connection struct {
-	stor IStorage                // underlying storage
 	db   *DB                     // Connection is part of this DB
 	txn  transaction.Transaction // opened under this txn; nil if idle in DB pool.
 	at   Tid                     // current view of database; stable inside a transaction.
@@ -137,7 +136,6 @@ type LiveCacheControl interface {
 // newConnection creates new Connection associated with db.
 func newConnection(db *DB, at Tid) *Connection {
 	return &Connection{
-		stor:  db.stor,
 		db:    db,
 		at:    at,
 		cache: LiveCache{
@@ -262,7 +260,7 @@ func (conn *Connection) Get(ctx context.Context, oid Oid) (_ IPersistent, err er
 // load loads object specified by oid.
 func (conn *Connection) load(ctx context.Context, oid Oid) (_ *mem.Buf, serial Tid, _ error) {
 	conn.checkTxnCtx(ctx, "load")
-	return conn.stor.Load(ctx, Xid{Oid: oid, At: conn.at})
+	return conn.db.stor.Load(ctx, Xid{Oid: oid, At: conn.at})
 }
 
 // ----------------------------------------

go/zodb/zodbpy.go

-// Copyright (C) 2018  Nexedi SA and Contributors.
-//                     Kirill Smelkov <kirr@nexedi.com>
+// Copyright (C) 2018-2019  Nexedi SA and Contributors.
+//                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
 // it under the terms of the GNU General Public License version 3, or (at your
@@ -74,7 +74,7 @@ func pySetState(obj PyStateful, objClass string, state *mem.Buf, jar *Connection
 // It only returns decoded database data.
 func (conn *Connection) loadpy(ctx context.Context, oid Oid) (class string, pystate interface{}, serial Tid, _ error) {
 	xid := Xid{Oid: oid, At: conn.at}
-	buf, serial, err := conn.stor.Load(ctx, xid)
+	buf, serial, err := conn.db.stor.Load(ctx, xid)
 	if err != nil {
 		return "", nil, 0, err
 	}
@@ -84,7 +84,7 @@ func (conn *Connection) loadpy(ctx context.Context, oid Oid) (class string, pyst
 	pyclass, pystate, err := PyData(buf.Data).decode(conn)
 	if err != nil {
 		err = &OpError{
-			URL:  conn.stor.URL(),
+			URL:  conn.db.stor.URL(),
 			Op:   "loadpy",
 			Args: xid,
 			Err:  err,