Server crashes if a flush commmand is issued and binlog is closed.
- added check to prevent binlog access when binlog file isn't opened.


sql/sql_parse.cc:
  - removed deprecated environment consistency check.
  - added check to prevent binlog access on closed binlog.
mysql-test/t/flush2-master.opt:
  - Added test case (master options)
mysql-test/t/flush2.test:
  - Added test case
mysql-test/r/flush2.result:
  - Added test case (resultfile)