tables open

When executing a DROP DATABASE statement in ROW mode and having temporary
tables open at the same time, the existance of temporary tables prevent
the server from switching back to row mode after temporarily switching to
statement mode to handle the logging of the statement.

Fixed the problem by removing the code to switch to statement mode and added
code to temporarily disable the binary log while dropping the objects in the
database.


mysql-test/extra/binlog_tests/database.test:
  Added test to ensure that DROP DATABASE does not affect the replication mode.
sql/sql_db.cc:
  Removed code that clears the current_stmt_binlog_row_based flag.
  Added code to disable the binary log while dropping the objects
  in a database.