[xml] XPath child axis traversal is broken when docb is disabled (libxml2 2.6.27)

[Aleksey Sanin <aleksey aleksey com>]

If you compile libxml2 with "--without-docb" option then
XPath child axis traversal is broken due to the following
ifdef in the xmlXPathNextDescendantOrSelfElemParent()
function:

	while (cur != NULL) {
	    switch (cur->type) {
		case XML_ELEMENT_NODE:
		/* TODO: OK to have XInclude here? */
		case XML_XINCLUDE_START:
		case XML_DOCUMENT_FRAG_NODE:		
		    if (cur != start)
			return(cur);
		    if (cur->children != NULL) {
			cur = cur->children;
			continue;
		    }
		    break;
#ifdef LIBXML_DOCB_ENABLED
		/* Not sure if we need those here. */
		case XML_DOCUMENT_NODE:
		case XML_DOCB_DOCUMENT_NODE:
#endif
		case XML_HTML_DOCUMENT_NODE:
		    if (cur != start)
			return(cur);
		    return(xmlDocGetRootElement((xmlDocPtr) cur));
		default:
		    break;
	    }	

It seems that the right thing to do is to simply move the
"case XML_DOCUMENT_NODE:" out of this particular ifdef but
I am not familiar enough with DOCB stuff to tell the consequences
of this.

Best,
Aleksey