don't let after_update block after_delete unless actually updating a counter

we use counter_culture, [rails3_acts_as_paranoid](https://github.com/goncalossilva/rails3_acts_as_paranoid) and [userstamp](https://github.com/insphire/userstamp) together.

Upon deletion of an object, userstamp updates the deleted_by column thus triggering a counter_culture after_update callback. 

That callback prevents the after_delete callback from firing when acts_as_paranoid updates the deleted_at timestamp.

The after_update callback should not block further callbacks unless its actually going to change the count.

As we don't use any conditional counters, I'm not sure if the proposed change will cause any race conditions