Import ignore_window code from mysql_replication plugin

We have a need to be able to monitor that backups are running ( not as ideal as 'completed successfully', but a start ) on our db servers.  The simplest way to do it is with this plugin matching the script name. 

This PR imports the "ignore_window" code from the mysql_replication_monitor plugin to allow us to name the time period during which we expect the backup process to be running, and alert if it isn't.