Fix autoderef of function calls when the function is not an lval.

As it turns out, the correct way to handle this is much simpler than what I
did originally.
Also add more tests.

src/test/run-pass/auto-deref-fn.rs

@@ -8,4 +8,5 @@ fn main() {
     assert(f(5) == 6);
     assert(g(8) == 9);
     assert(h(0x1badd00d) == 0x1badd00e);
+    assert((@add1)(42) == 43);
 }

src/test/run-pass/call-autoderef-tag.rs

@@ -0,0 +1,11 @@
+// xfail-stage0
+tag int_fn { f(fn(int) -> int); }
+tag int_box_fn { fb(@fn(int) -> int); }
+fn add1(int i) -> int { ret i+1; }
+fn main() {
+    auto g = f(add1);
+    assert(g(4) == 5);
+    assert((f(add1))(5) == 6);
+    assert((@(f(add1)))(5) == 6);
+    assert((fb(@add1))(7) == 8);
+}