swarm/network: fix chunk integrity checks (#3665)

* swarm/network: integrity on incoming known chunks
* swarm/network: fix integrity check for incoming chunks
* swarm/storage: imrpoved integrity checking on chunks
* dbstore panics on corrupt chunk entry an prompts user to run cleandb
* memstore adds logging for garbage collection
* dbstore refactor item delete. correct partial deletes in Get
* cmd/swarm: added cleandb subcommand

cmd/swarm/main.go

@@ -191,6 +191,15 @@ Removes a path from the manifest
 				},
 			},
 		},
+		{
+			Action:    cleandb,
+			Name:      "cleandb",
+			Usage:     "Cleans database of corrupted entries",
+			ArgsUsage: " ",
+			Description: `
+Cleans database of corrupted entries.
+`,
+		},
 	}
 
 	app.Flags = []cli.Flag{