auto merge of #6302 : nikomatsakis/rust/issue-6141-leaking-owned-fn, r=brson

When autoborrowing a fn in trans, adjust the type of the datum to be `&fn`.

Fixes #6141.

r? @brson

src/test/run-pass/issue-6141-leaking-owned-fn.rs

@@ -0,0 +1,8 @@
+fn run(f: &fn()) {
+    f()
+}
+
+fn main() {
+    let f: ~fn() = || ();
+    run(f);
+}