Add regression test for duplicate items in overlapping impls. Note that a...

Add regression test for duplicate items in overlapping impls. Note that a regression test already exists for *non*overlapping impls.

src/test/compile-fail/inherent-overlap.rs

+// Copyright 2016 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 that you cannot define items with the same name in overlapping inherent
+// impl blocks.
+
+struct Foo;
+
+impl Foo {
+    fn id() {} //~ ERROR E0201
+}
+
+impl Foo {
+    fn id() {}
+}
+
+struct Bar<T>(T);
+
+impl<T> Bar<T> {
+    fn bar(&self) {} //~ ERROR E0201
+}
+
+impl Bar<u32> {
+    fn bar(&self) {}
+}
+
+struct Baz<T>(T);
+
+impl<T: Copy> Baz<T> {
+    fn baz(&self) {} //~ ERROR E0201
+}
+
+impl<T> Baz<Vec<T>> {
+    fn baz(&self) {}
+}
+
+fn main() {}