Various fixes for XML PARSE.

Various fixes for XML PARSE.

Annotate unused parameters.  Do not compile some functions that might
not be needed.  Consistent with libgcobol, log errors via syslog(3).
Introduce push-parser as experiment.

libgcobol/ChangeLog: Correct warnings and errors in xmlparse.cc.

	* xmlparse.cc (CTX): Macro for unused user-context parameter.
	(attributeDecl): Mark unused parameters.
	(cdataBlock): Same.
	(characters): Same.
	(comment): Same.
	(elementDecl): Same.
	(endDocument): Same.
	(endElementNs): Same.
	(endElement): Same.
	(entityDecl): Same.
	(error): Same.
	(externalSubset): Same.
	(fatalError): Same.
	(getEntity): Eliminate via preprocessor until needed.
	(getParameterEntity): Same.
	(hasExternalSubset): Mark unused parameters.
	(hasInternalSubset): Same.
	(ignorableWhitespace): Same.
	(internalSubset): Same.
	(isStandalone): Eliminate via preprocessor until needed.
	(notationDecl): Mark unused parameters.
	(processingInstruction): Same.
	(reference): Same.
	(resolveEntity): Eliminate via preprocessor until needed.
	(setDocumentLocator): Mark unused parameters.
	(startDocument): Same.
	(startElementNs): Same.
	(startElement): Same.
	(unparsedEntityDecl): Same.
	(warning): Same.
	(xmlchar_of): Utility cast function.
	(xmlParserErrors_str): Message string for libxml2 errors.
	(xmlerror_str): Macro to include textual form of libxml2 error.
	(context_t): Push-parser context class.
	(xml_push_parse): Use push-parser.
	(__gg__xml_parse_done): Signify end-of-input to XML push-parser.
	(__gg__xml_parse): Mark unused parameters.