** I already fixed it in 3.23; I fix it in 4.0 separately because the
code is a bit different (so the changeset 1.1422 of 3.23 should not be
merged here) **
Make mysqlbinlog prompt for the password if
mysqlbinlog -p
instead of printing the usage().
This makes mysqlbinlog behave like other clients.
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).