aggregator_expire: run entire invocation loop under lock
aggregator_expire: run entire invocation loop under lock

Access to the invocation buckets happens concurrently, so we need to
lock down the entire loop to make it safe.  A better strategy for
aggregations is necessary.

grobian/carbon-c-relay,piotr1212/carbon-c-relay,piotr1212/carbon-c-relay,piotr1212/carbon-c-relay,grobian/carbon-c-relay,grobian/carbon-c-relay,piotr1212/carbon-c-relay