WL#1721: a binary format for master.info and relay-log.info

Affects: Server-7.1   —   Status: Un-Assigned   —   Priority: Medium

Instead of writing positions in human-readable format in master.info (same
applies for relay-log.info) using sprintf("%d"), write the position in binary
format (int4store, int8store). Should make a faster
When the user wants to see the position from the master.info, have a command in
mysqladmin decode-replication-info-file the_file