XFAIL comm-2 for now; there's an assertion trappping in rust_task::wakeup.

src/Makefile

@@ -376,6 +376,7 @@ TEST_XFAILS_X86 :=  $(MUT_BOX_XFAILS) \
                     test/run-pass/task-comm.rs \
                     test/run-pass/vec-alloc-append.rs \
                     test/run-pass/vec-slice.rs \
+                    test/run-pass/task-comm-2.rs \
                     test/run-pass/task-comm-3.rs \
                     test/compile-fail/bad-recv.rs \
                     test/compile-fail/bad-send.rs \