Send replication errors as strings if JSON encoding fails
Send replication errors as strings if JSON encoding fails

Part of r996493, see COUCHDB-884, original patch by Filipe Manana.

BugzID: 11789

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb