Backup folders on network shares often refuse SQLite's file locks (CIFS
without nobrl, NFS without lockd). SQLite reports a refused lock as
SQLITE_BUSY, so every backup to such a folder retried until the 60 second
give-up and blamed a locked database, while the live database was not
locked at all (#1246).
The target is a scratch .pending file that nothing else opens, so open it
with nolock=1. The give-up message now names the live database, since that
is the only file a backup can still wait on.