Add test for issue 868

Author: catamorphism

src/test/run-pass/issue-868.rs

@@ -0,0 +1,15 @@
+fn f<T>(g: fn() -> T) -> T { g() }
+
+fn main() {
+  let _x = f( | | { 10 });
+    // used to be: cannot determine a type for this expression
+    f(| | { });
+    // ditto
+    f( | | { ()});
+    // always worked
+    let _: () = f(| | { });
+    // empty block with no type info should compile too
+    let _ = f(||{});
+    let _ = (||{});
+}
+