Problem: In mixed replication, events that has unsafe functions
(sysdate()) cannot be created.

Analysis: DDL Statements (that change metadata) are always
getting written in the binlog in STATEMENT format irrespective
of binlog_format settings. And the changes to the metadata
should not be replicated as the same statement when it is executed
on Slave will update the metadata on slave side. Event based SQL
commands (CREATE EVENT, ALTER EVENT and DROP EVENT) belong to
the same category. Code was written to take care of changing the
current_statement_binlog_format into 'statement' if it is 'row'
in case of executing/replicating such statements. But in case of
create event and alter event, after we are converting row format
to statement format, while we are opening the tables server decides
the binlogging format (in decide_binlog_format()) and the logic
again changes binlog format to "row" if it sees the statement is
unsafe and we are using mixed format.

Fix: Reset the thd.variables.binlog_format to 'statement' before create/alter
events work when we are clearning current_statement_binlog_format.
And set it back to the original value at the end of the work.