mk_filter: Fix push output handling.
mk_http: Increase number of iovec entries in mk_http_queue_send().
mk_queue: Fix loop condition in mk_queue_iovec().
deflate: Limit idle context count to MK_COMPRESS_IDLE_LIMIT.
mk_filter: Use filter_end() for continue calls.

Only call filter when data available, and allow filter_end to be called
multiple times if MK_FILTER_CONTINUE is returned.
mk_plugin_next: Add mk_response_info struct.
mk_plugin_next: Filter prototype changed.
mk_http_transport: Continue in filter_end and use response info.
deflate: Continue in filter_end and use response info.