Split TyBareFn into TyFnDef and TyFnPtr.

There's a lot of stuff wrong with the representation of these types:
TyFnDef doesn't actually uniquely identify a function, TyFnPtr is used to
represent method calls, TyFnDef in the sub-expression of a cast isn't
correctly reified, and probably some other stuff I haven't discovered yet.
Splitting them seems like the right first step, though.

src/test/compile-fail/invalid-intrinsic.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(intrinsics)]
+extern "rust-intrinsic" {
+    pub static breakpoint : unsafe extern "rust-intrinsic" fn();
+    //~^ ERROR intrinsic has wrong type
+}
+fn main() { unsafe { breakpoint(); } }

src/test/compile-fail/variadic-ffi-3.rs

@@ -22,7 +22,7 @@ fn main() {
         let x: unsafe extern "C" fn(f: isize, x: u8) = foo;
         //~^ ERROR: mismatched types
         //~| expected `unsafe extern "C" fn(isize, u8)`
-        //~| found `unsafe extern "C" fn(isize, u8, ...)`
+        //~| found `unsafe extern "C" fn(isize, u8, ...) {foo}`
         //~| expected non-variadic fn
         //~| found variadic function