act immediately on weave connecting existing addresses

we simply reset the vars controlling backoff for that address
Note that we do not interrupt any current connection attempt, since
that is hard.

Closes #499.

router/connection_maker.go

@@ -48,6 +48,9 @@ func (cm *ConnectionMaker) Start() {
 func (cm *ConnectionMaker) InitiateConnection(address string) {
 	cm.actionChan <- func() bool {
 		cm.cmdLineAddress[NormalisePeerAddr(address)] = true
+		if target, found := cm.targets[address]; found {
+			target.tryAfter, target.tryInterval = tryImmediately()
+		}
 		return true
 	}
 }