Implement serf_bucket_get_remaining() for LIMIT buckets.
Implement serf_bucket_get_remaining() for LIMIT buckets.

* buckets/limit_buckets.c
  (serf_limit_get_remaining): New.
  (serf_bucket_type_limit): Add serf_limit_get_remaining().

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