xinclude: Improve error handling

Introduce xmlXIncludeSetErrorHandler allowing to set a structured error
handler for an XInclude context and forwarding errors from parser.

Remove arguments from memory error handlers.

Use xmlRaiseMemoryError.

include/libxml/xinclude.h

@@ -115,6 +115,10 @@ XMLPUBFUN xmlXIncludeCtxtPtr
 XMLPUBFUN int
 		xmlXIncludeSetFlags	(xmlXIncludeCtxtPtr ctxt,
 					 int flags);
+XMLPUBFUN void
+		xmlXIncludeSetErrorHandler(xmlXIncludeCtxtPtr ctxt,
+					 xmlStructuredErrorFunc handler,
+					 void *data);
 XMLPUBFUN int
 		xmlXIncludeGetLastError	(xmlXIncludeCtxtPtr ctxt);
 XMLPUBFUN void