Add a test for issue #2312

Author: brson

src/test/run-pass/issue-2312.rs

@@ -0,0 +1,11 @@
+// Testing that the B's are resolved
+
+trait clam<A> { }
+
+enum foo = int;
+
+impl foo {
+    fn bar<B,C:clam<B>>(c: C) -> B { fail; }
+}
+
+fn main() { }