cmd/syncthing, lib/db, lib/model, lib/protocol: Implement delta indexes (fixes #438)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3427

cmd/syncthing/main.go

@@ -682,17 +682,9 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 		}
 	}
 
-	// Clear out old indexes for other devices. Otherwise we'll start up and
-	// start needing a bunch of files which are nowhere to be found. This
-	// needs to be changed when we correctly do persistent indexes.
+	// Add and start folders
 	for _, folderCfg := range cfg.Folders() {
 		m.AddFolder(folderCfg)
-		for _, device := range folderCfg.DeviceIDs() {
-			if device == myID {
-				continue
-			}
-			m.Index(device, folderCfg.ID, nil)
-		}
 		m.StartFolder(folderCfg.ID)
 	}