Several small fixes.

* [DCG_COPYRIGHT,FIX] Fixed two typos.
* [DCG_PRINT,FIX] Fixed nameing conflict with DCG_DICT.
* [DEB] New directories OS and DCG are now loaded in the documentation server.
* [DIR_EXT,FIX] Added missing module import.
* [META_EXT,FIX] Added missing module import.
* [RDF_GRAPH,FIX] Added missing module import.
* [XML_STREAM,NEW] Added wrapper xml_stream/3.