Integrity checker could manage subscripton permission revocation more clearly

Hello all,

please consider the following scenario:

1. JIRA is deployed standalone and users and groups are created in the internal database
2. filters are shared - among groups, in particular and subscriptions to these are enabled
3. JIRA is then subsequently integrated with Crowd and some of these groups are lost in the process
4. the integrity checker will report the following message rather than correctly identify a subscription to a filter shared with a non-existent group:

   Subscription filter with id #### is missing its corresponding saved filter and will be removed
   

It would be desirable if the integrity checker would:

1. check for filters shared to non existing users/groups
2. perform more context as to why the filter is now missing and should be removed

Best Regards,
Edoardo