Bring run-pass/spawn-fn up to date and un-XFAIL

src/test/run-pass/spawn-fn.rs

@@ -1,8 +1,8 @@
-// xfail-stage1
-// xfail-stage2
-// xfail-stage3
 // -*- rust -*-
 
+use std;
+import std::task::yield;
+
 fn x(s: str, n: int) { log s; log n; }
 
 fn main() {
@@ -10,5 +10,5 @@ fn main() {
     spawn x("hello from second spawned fn", 66);
     spawn x("hello from third spawned fn", 67);
     let i: int = 30;
-    while i > 0 { i = i - 1; log "parent sleeping"; yield; }
+    while i > 0 { i = i - 1; log "parent sleeping"; yield(); }
 }