IsLocalHost: support host:port

Without this patch IsLocalHost does not work for URLs with port specified i.e. it works for `http://localhost` but does not work for `http://localhost:80` or `http://localhost:10000`.

Fixes #487

dispatcher.go

@@ -102,10 +102,8 @@ var localHostIpv4 = regexp.MustCompile(`127\.0\.0\.\d+`)
 // IsLocalHost checks whether the destination host is explicitly local host
 // (buggy, there can be IPv6 addresses it doesn't catch)
 var IsLocalHost ReqConditionFunc = func(req *http.Request, ctx *ProxyCtx) bool {
-	return req.URL.Host == "::1" ||
-		req.URL.Host == "0:0:0:0:0:0:0:1" ||
-		localHostIpv4.MatchString(req.URL.Host) ||
-		req.URL.Host == "localhost"
+	h := req.URL.Hostname()
+	return h == "::1" || h == "0:0:0:0:0:0:0:1" || localHostIpv4.MatchString(h) || h == "localhost"
 }
 
 // UrlMatches returns a ReqCondition testing whether the destination URL