Several changes to the check-config mode for Cisco IOS systems.

I didn't find the check usefull as it was. When doing a simple "sh run" on the device to check the current config (or doing automated remote backups,) the check started to spit out warnings, etc. Now it only does so when you've entered config mode. This still doesn't check if the running config is truely different from the startup config, but that cannot be done through SNMP for as far as I know.
Changes:

* Modified config check to only take the running-config-changed and the startup-config-changed
values into account. (The running-config-saved value is not usefull for this check)
* Added a time-margin after a reload (5 minutes seems reasonable) wherein the running-config-changed time
may be ahead of the startup-config-changed time. After a reload, the device may report a
running-config-changed time of up to 5 minutes later than the startup-config-changed time when
in fact nothing has changed.
* Fixed mitigation; this parameter had no effect.