Problem: mysqlbinlog_base64 fails because the binlog contains
traces from previous test cases.
Fix: Make have_log_bin reset the master's binlog.


mysql-test/include/have_log_bin.inc:
  Made have_log_bin reset the master logs, so that no traces of
  earlier test cases are left.
mysql-test/t/mysqlbinlog_base64.test:
  Removed debug info from previous push to this test.