Various fixes upon loading *all* PGC modules, attempting to sync all modules to the latest changes.

* [FIX] Many missing module imports and other fixes.
* [DCG_CONTENT,NEW] Added void//0.
* [RDF_VOCABULARY,SC] Updated this module. Removed RDFS.RDF.
* [RFC2616_BASIC,NEW] Added HT//1, SP//1.
* [RFC4234_ABNF,SC] Removed.
* [RFC4234_BASIC,NEW] Added 1*BIT//1, WSP//1.
* [WORDNET,WORDNET_WEB,SC] Updated Wordnet support with DCGs.