mysql plugin: Added support for master/slave statistics.

mysql plugin: Added support for master/slave statistics.

MySQL replication master and slave statistics may be enabled using the newly
added boolean config options "MasterStats" and "SlaveStats". In the first
case, the position in the binlog is collected while in the later case the
read and exec positions in the master log as well as the value of the
Seconds_Behind_Master variable are collected.

For the log positions, the counter type "mysql_log_position" has been
introduced while "time_offset" is used for the Seconds_Behind_Master values.