Test for issue 2735

This probably doesn't test the actual bug, but the fix for
issue 2734 probably camouflages the actual bug (since the
effect of the #2734 test case is now "do nothing observable"
rather than "segfault").

Closes #2735

src/test/run-pass/issue-2735.rs

@@ -0,0 +1,14 @@
+iface hax { } 
+impl <A> of hax for A { } 
+
+fn perform_hax<T>(x: @T) -> hax {
+    x as hax 
+}
+
+fn deadcode() {
+    perform_hax(@"deadcode");
+}
+
+fn main() {
+    perform_hax(@42);
+}