Better handling of ensuring that setup_tables() are not called twice

This fixed a bug in prepared statements when used with outher joins
Fixed a bug in SUM(DISTINCT) when used with prepared statements.
Some safety fixes in test scripts to ensure that previous test failures shouldn't affect other tests

mysql-test/r/synchronization.result

@@ -1,3 +1,4 @@
+drop table if exists t1;
 CREATE TABLE t1 (x1 int);
  ALTER TABLE t1 CHANGE x1 x2 int;
 CREATE TABLE t2 LIKE t1;