Add test for issue 2467

Author: catamorphism

src/test/compile-fail/issue-2467.rs

@@ -0,0 +1,6 @@
+enum test { thing = 3u } //! ERROR mismatched types
+//!^ ERROR expected signed integer constant
+fn main() {
+    log(error, thing as int);
+    assert(thing as int == 3);
+}