new test showing off the improved inference

src/test/run-pass/closure-inference.rs

@@ -0,0 +1,8 @@
+fn foo(i: int) -> int { i + 1 }
+
+fn apply<A>(f: fn(A) -> A, v: A) -> A { f(v) }
+
+fn main() {
+    let f = {|i| foo(i)};
+    assert apply(f, 2) == 3;
+}