Play nice when ACME used manually.

Minor change to server/server.go such that /.well-known/acme-challenge
can be passed through when TLS.Manual is true on the vhost the request
came in through.

server/server.go

@@ -296,11 +296,6 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	w.Header().Set("Server", "Caddy")
 
-	// Execute the optional request callback if it exists
-	if s.ReqCallback != nil && s.ReqCallback(w, r) {
-		return
-	}
-
 	host, _, err := net.SplitHostPort(r.Host)
 	if err != nil {
 		host = r.Host // oh well
@@ -315,6 +310,11 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	// Execute the optional request callback if it exists and it's not disabled
+	if s.ReqCallback != nil && !s.vhosts[host].config.TLS.Manual && s.ReqCallback(w, r) {
+		return
+	}
+
 	if vh, ok := s.vhosts[host]; ok {
 		status, _ := vh.stack.ServeHTTP(w, r)