Fix gcc "no previous prototype" warnings after reorganisation:

* server/core_filters.c (ap_core_input_filter, ap_core_output_filter,
ap_net_time_filter): Renamed to add ap_ prefixes for global symbols.

* include/ap_listen.h: Don't export ap_listen_open at all, it's not
used outside server/listen.c any more.

* server/listen.c (open_listeners): Renamed from ap_listen_open.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@109498 13f79535-47bb-0310-9956-ffa450edef68