Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/google.golang.org/appengine/internal/main_vm.go

@@ -22,7 +22,11 @@ func Main() {
 		port = s
 	}
 
-	if err := http.ListenAndServe(":"+port, http.HandlerFunc(handleHTTP)); err != nil {
+	host := ""
+	if IsDevAppServer() {
+		host = "127.0.0.1"
+	}
+	if err := http.ListenAndServe(host+":"+port, http.HandlerFunc(handleHTTP)); err != nil {
 		log.Fatalf("http.ListenAndServe: %v", err)
 	}
 }