Two minor fixes:
 1. to make make test executes with mixed;
 2. proper isolation of binlog_statement_insert_delayed 
    from others through reset master cleaning up binlog
    todo: adapt this technique to other restarting for binlog tests


Makefile.am:
  Binlog format switches to MIXED. A new Makefile target
  test-binlog-statement 
  is introduced for checking tests requiring exclusive STATEMENT format.
mysql-test/t/binlog_statement_insert_delayed.test:
  cheapest method to clean up binlog after previous tests