Add infrastructure for compiletests

Also adds compilefail tests for some lints, closes #5646.

tests/compiletest/plugin/compile-fail/ban.rs

@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![feature(plugin)]
+#![plugin(plugins)]
+
+extern crate js;
+
+use js::jsval::JSVal;
+use std::cell::Cell;
+
+struct Foo {
+    bar: Cell<JSVal>
+    //~^ ERROR Banned type Cell<JSVal> detected. Use MutHeap<JSVal> instead,
+}
+
+fn main() {}