Fixed failing test cases and compiler warnings found by buildbot

- Added some extra command to rpl_start_stop to ensure that the
  IO thread has connected to the master before we shut down the server.
- if signal returns signalhandler_t, use this with the alarm code
- Added missing tests to sys_vars
- Fixed some possible overflow bugs in tabxml.cpp

mysql-test/suite/rpl/r/rpl_start_stop_slave.result

@@ -8,4 +8,6 @@ set @time_after_kill := (select CURRENT_TIMESTAMP);
 [Time after the query]
 [Killing of the slave IO thread was successful]
 START SLAVE IO_THREAD;
+create table t1 (a int primary key);
+drop table t1;
 include/rpl_end.inc