Adding recording of both master and slave binlog positions when possible

When taking a backup from a mysql slave server there may be some confusion as to which binlog position to record. If we intend to create a slave of this slave's master, we will want to use the slave position, but if we intend to create a slave of this slave - we will want to record the master position and ignore the slave position. What is worse, we may not know what we intend to use this snapshot for until later. So, to make this simple and flexible we can record BOTH master and slave position into (now slightly misnamed) master status file - allowing us to use either set of positions at restore time. To aid in automation of the new slave deployment,  I also added recording of the hostnames the positions refer to.

NOTE: This has potential to confuse existing automation as the master_log_file/pos parameters in master status file will now always refer to master position.