Add support for MySQL binary logging in mysqldump

If binary logging is enabled in my.cnf it is broadly recommended to
add the "--master-data=2" parameter to mysqldump so that binary log
position information is included in the dump file for PITR.

I tested modifying the files from a v1 release install. I'm speculating that 
config-defaults.rb is the right place to add the new option. Apologies 
if not.