Write Protocol version to the db so we can perform sanity checks

ethereum.go

@@ -90,7 +90,6 @@ type Ethereum struct {
 }
 
 func New(db ethutil.Database, clientIdentity ethwire.ClientIdentity, keyManager *ethcrypto.KeyManager, caps Caps, usePnp bool) (*Ethereum, error) {
-
 	var err error
 	var nat NAT
 
@@ -101,6 +100,8 @@ func New(db ethutil.Database, clientIdentity ethwire.ClientIdentity, keyManager
 		}
 	}
 
+	bootstrapDb(db)
+
 	ethutil.Config.Db = db
 
 	nonce, _ := ethutil.RandomUint64()
@@ -534,3 +535,12 @@ out:
 		}
 	}
 }
+
+func bootstrapDb(db ethutil.Database) {
+	d, _ := db.Get([]byte("ProtocolVersion"))
+	protov := ethutil.NewValue(d).Uint()
+
+	if protov == 0 {
+		db.Put([]byte("ProtocolVersion"), ethutil.NewValue(ProtocolVersion).Bytes())
+	}
+}