consider DepNode::Krate to be an input

This seems not only more correct but allows us to write tests that check
whether the krate hash as a whole is clean/dirty

src/test/incremental/crate_hash_reorder.rs

@@ -0,0 +1,40 @@
+// Copyright 2014 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.
+
+// Test incremental compilation tracking where we change field names
+// in between revisions (hashing should be stable).
+
+// revisions:rpass1 rpass2 rpass3
+// compile-flags: -Z query-dep-graph
+
+#![feature(rustc_attrs)]
+
+// Check that reordering otherwise identical items is not considered a
+// change at all.
+#[rustc_clean(label="Krate", cfg="rpass2")]
+
+// But removing an item, naturally, is.
+#[rustc_dirty(label="Krate", cfg="rpass3")]
+
+#[cfg(rpass1)]
+pub struct X {
+    pub x: u32,
+}
+
+pub struct Y {
+    pub x: u32,
+}
+
+#[cfg(rpass2)]
+pub struct X {
+    pub x: u32,
+}
+
+pub fn main() { }