Add test to ensure auto-traits are respecting constraints

Author: GuillaumeGomez

src/test/rustdoc/auto-trait-not-send.rs

@@ -0,0 +1,8 @@
+#![crate_name = "foo"]
+
+// @has 'foo/struct.Foo.html'
+// @has - '//*[@id="impl-Send"]' 'impl !Send for Foo'
+// @has - '//*[@id="impl-Sync"]' 'impl !Sync for Foo'
+pub struct Foo(*const i8);
+pub trait Whatever: Send {}
+impl<T: Send + ?Sized> Whatever for T {}