mod+kvdb+channeldb: use btcwallet new DB interface

Depends on btcsuite/btcwallet#757.
Pulls in the updated version of btcwallet and walletdb that have the DB
interface enhanced by their own View() and Update() methods with the
reset callback/closure supported out of the box. That way the global
package-level View() and Update() functions now become pure redirects.

kvdb/interface.go

@@ -13,12 +13,7 @@ import (
 // database backend used), the reset function will be called before each retry
 // respectively.
 func Update(db Backend, f func(tx RwTx) error, reset func()) error {
-	if extendedDB, ok := db.(ExtendedBackend); ok {
-		return extendedDB.Update(f, reset)
-	}
-
-	reset()
-	return walletdb.Update(db, f)
+	return db.Update(f, reset)
 }
 
 // View opens a database read transaction and executes the function f with the
@@ -29,15 +24,7 @@ func Update(db Backend, f func(tx RwTx) error, reset func()) error {
 // expect retries of the f closure (depending on the database backend used), the
 // reset function will be called before each retry respectively.
 func View(db Backend, f func(tx RTx) error, reset func()) error {
-	if extendedDB, ok := db.(ExtendedBackend); ok {
-		return extendedDB.View(f, reset)
-	}
-
-	// Since we know that walletdb simply calls into bbolt which never
-	// retries transactions, we'll call the reset function here before View.
-	reset()
-
-	return walletdb.View(db, f)
+	return db.View(f, reset)
 }
 
 // Batch is identical to the Update call, but it attempts to combine several
@@ -46,10 +33,12 @@ func View(db Backend, f func(tx RTx) error, reset func()) error {
 // Batch. For etcd Batch simply does an Update since combination is more complex
 // in that case due to STM retries.
 func Batch(db Backend, f func(tx RwTx) error) error {
-	if extendedDB, ok := db.(ExtendedBackend); ok {
+	// Fall back to the normal Update method if the backend doesn't support
+	// batching.
+	if _, ok := db.(walletdb.BatchDB); !ok {
 		// Since Batch calls handle external state reset, we can safely
 		// pass in an empty reset closure.
-		return extendedDB.Update(f, func() {})
+		return db.Update(f, func() {})
 	}
 
 	return walletdb.Batch(db, f)
@@ -66,35 +55,6 @@ var Create = walletdb.Create
 // through read or read+write transactions.
 type Backend = walletdb.DB
 
-// ExtendedBackend is and interface that supports View and Update and also able
-// to collect database access patterns.
-type ExtendedBackend interface {
-	Backend
-
-	// PrintStats returns all collected stats pretty printed into a string.
-	PrintStats() string
-
-	// View opens a database read transaction and executes the function f
-	// with the transaction passed as a parameter. After f exits, the
-	// transaction is rolled back. If f errors, its error is returned, not a
-	// rollback error (if any occur). The passed reset function is called
-	// before the start of the transaction and can be used to reset
-	// intermediate state. As callers may expect retries of the f closure
-	// (depending on the database backend used), the reset function will be
-	//called before each retry respectively.
-	View(f func(tx walletdb.ReadTx) error, reset func()) error
-
-	// Update opens a database read/write transaction and executes the
-	// function f with the transaction passed as a parameter. After f exits,
-	// if f did not error, the transaction is committed. Otherwise, if f did
-	// error, the transaction is rolled back. If the rollback fails, the
-	// original error returned by f is still returned. If the commit fails,
-	// the commit error is returned. As callers may expect retries of the f
-	// closure (depending on the database backend used), the reset function
-	// will be called before each retry respectively.
-	Update(f func(tx walletdb.ReadWriteTx) error, reset func()) error
-}
-
 // Open opens an existing database for the specified type. The arguments are
 // specific to the database type driver. See the documentation for the database
 // driver for further details.
@@ -129,9 +89,8 @@ type RwBucket = walletdb.ReadWriteBucket
 // operations.
 type RwCursor = walletdb.ReadWriteCursor
 
-// ReadWriteTx represents a database transaction that can be used for both
-// reads and writes. When only reads are necessary, consider using a RTx
-// instead.
+// RwTx represents a database transaction that can be used for both reads and
+// writes. When only reads are necessary, consider using a RTx instead.
 type RwTx = walletdb.ReadWriteTx
 
 var (