futures: tests/select_all.rs: Don't break w/o "executor"
Symbols/Imports pushed down / localised
Tests gated with cfg()
Tests now build and pass with all valid feature combinations
See previous commits for details and rationale
+#[cfg(feature = "executor")] // executor::
+#[test]
+fn smoke() {
use futures::executor::block_on;
use futures::future::{ready, select_all};
use std::collections::HashSet;
-#[test]
-fn smoke() {
let v = vec![
ready(1),
ready(2),
