There are some problems about help text:
- It is stated that "auto" is the default twice. It need be stated only once.
- It is stated that --base64-output is short for --base64-output=always. But that sounds
like the default is "always", not "auto".

Make the help text clear as following:
Determine when the output statements should be base64-encoded BINLOG 
statements: 'never' disables it and works only for binlogs without 
row-based events; 'auto' prints base64 only when necessary (i.e., 
for row-based events and format description events); 'always' prints 
base64 whenever possible. 'always' is for debugging only and should 
not be used in a production system. If this argument is not given, 
the default is 'auto'; if it is given with no argument, 'always' is used.