Make mysqlbinlog prompt for the password if
mysqlbinlog -p
instead of printing the usage().
This makes mysqlbinlog behave like other clients, which is the reason
why we fix this in 3.23.
This new code was almost copied from mysqldump.
Note that before, one could use
mysqlbinlog -p pass
and now one must use
mysqlbinlog -ppass
(putting a space will ask for the password).