util_filter: keep filters with aside buckets in order.

Read or write of filter's pending data must happen in the same order as the
filter chain, thus we can't use an apr_hash_t to maintain the pending filters
since it provides no garantee on this matter.

Instead use an APR_RING maintained in c->pending_filters, and since both the
name (was c->filters) and the type changed, MAJOR is bumped (trunk only code
anyway so far).



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1835640 13f79535-47bb-0310-9956-ffa450edef68