auto merge of #8223 : davidhalperin/rust/master, r=Aatch

Closes #7907

This is my first pull request so let me know if I've done anything wrong.  I tried to pick off a nice easy one.

src/test/compile-fail/conflicting-implementations.rs

@@ -0,0 +1,24 @@
+// Copyright 2013 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.
+
+// error-pattern: conflicting implementations for trait `Foo`
+trait Foo {
+}
+
+impl Foo for int {
+
+}
+
+impl<A> Foo for A {
+
+}
+
+fn main() {
+}