Fixed an issue where an aggregate with millions of child buckets gets very slow.
Fixed an issue where an aggregate with millions of
child buckets gets very slow.

* buckets/aggregate_buckets.c
  (aggregate_context_t): Keep a pointer to last bucket in
   the list.
  (serf_bucket_aggregate_become,
   serf_aggregate_restore_snapshot): Initiate 'last' ptr.
  (serf_bucket_aggregate_append): Use the 'last' ptr to 
   append at the end of the list, 

jandre/serf,jandre/serf,jandre/serf,jandre/serf