test: Add a test case for issue #362, "ret none".

Author: pcwalton

src/test/run-pass/ret-none.rs

@@ -0,0 +1,6 @@
+tag option[T] { none; some(T); }
+
+fn f[T]() -> option[T] { ret none; }
+
+fn main() { f[int](); }
+