1. Broader use of AP statistics tracking.
2. Improvements to RDF graph names support.

* [AP_STAT,EXT] Allow the potential number of applications to be set at a later stage. This is usefull when the custom goal is able to assess the number of potential applications, but the calling context is not.
* [RDF_AP,NEW] Added rdf_call_cleanup/3. Significant updates to the other predicates.
* [RDF_GRAPH,FIX] Ensure the merged graph does not already exist in rdf_graph_merge/2.
* [RDF_GRAPH_NAME,SC] New module, collecting predicates from RDF_GRAPH and RDF_SERIAL.
* [RDF_GRAPH_NAME,FIX] Make sure a new graph exists (even if it contains no triples).
* [USER_INPUT,EXT] Replaced the custom statistics tacking feature to use the AP statistics infrastructure.
Improved the statistics tracking for automated processes. Much simpler now, initialized from within a custom goal.

* [AP_ACT,EXT] Added statistics tracking for ap_merge_into_one_file/3.
* [AP_STAGE,SC] Removed options `actual` and `potential`.
* [AP_STAT,SC] Severely simplified the API.
Extensive cleanup of XML DOM code.

* [AP_STAGE,NEW] Added option between/2.
* [HTML,SC] Added setup_call_cleanup/3 and free DTD resource.
* [HTTP,XML_DOM,SC] Rewrote a lot of XML serving/converting predicates:
** Much less code.
** Much simpler API.
** Uses of setup_call_cleanup/3 and freeing of DTD resources.
** Use of dtd/2's internal file search procedure.
** Use of options to reduce the number of predicate variants.