Add test for copy image feature

Author: GuillaumeGomez

src/test/rustdoc/copy-local-img.rs

@@ -0,0 +1,10 @@
+#![crate_name = "foo"]
+
+// @has static/8a40d4987fbb905
+// @has foo/struct.Enum.html
+// @has - '//img[@src="../static/8a40d4987fbb905"]' ''
+
+/// Image test!
+///
+/// ![osef](src/test/rustdoc/copy-local-img.rs)
+pub struct Enum;