finish step 1
fix a bug in rpc layer: reply could be received before caching it in add_reply; pass test 9
remove some output in rpc layer; passed test 10
passed test 11
passed test 12
fix bug in primary_failure: we should keep trying until we got a new view; passed test 13
fix bug: invoke_mutex and rsm_mutex should overlap. passed test 16;
passed all tests (test 12 has little chance to fail).