Detect infinite recursion in parameter entities

When expanding a parameter entity in a DTD, infinite recursion could
lead to an infinite loop or memory exhaustion.

Thanks to Wei Lei for the first of many reports.

Fixes bug 759579.
xmlParseName(xmlParserCtxtPtr ctxt) {
    const xmlChar *in;
    const xmlChar *ret;
    int count = 0;

    GROW;

#ifdef DEBUG
    nbParseName++;
#endif

    /*
     * Accelerator for simple ASCII names
     */
    in = ctxt->input->cur;
    if (((*in >= 0x61) && (*in <= 0x7A)) ||
	((*in >= 0x41) && (*in <= 0x5A)) ||
	(*in == '_') || (*in == ':')) {
	in++;
	while (((*in >= 0x61) && (*in <= 0x7A)) ||
	       ((*in >= 0x41) && (*in <= 0x5A)) ||
	       ((*in >= 0x30) && (*in <= 0x39)) ||
	       (*in == '_') || (*in == '-') ||
	       (*in == ':') || (*in == '.'))
	    in++;
	if ((*in > 0) && (*in < 0x80)) {
	    count = in - ctxt->input->cur;
            if ((count > XML_MAX_NAME_LENGTH) &&
                ((ctxt->options & XML_PARSE_HUGE) == 0)) {
                xmlFatalErr(ctxt, XML_ERR_NAME_TOO_LONG, "Name");
                return(NULL);
            }
	    ret = xmlDictLookup(ctxt->dict, ctxt->input->cur, count);
	    ctxt->input->cur = in;
	    ctxt->nbChars += count;
	    ctxt->input->col += count;
	    if (ret == NULL)
	        xmlErrMemory(ctxt, NULL);
	    return(ret);
	}
    }
    /* accelerator for special cases */
    return(xmlParseNameComplex(ctxt));
}

xmlParseName(xmlParserCtxtPtr ctxt) {
    const xmlChar *in;
    const xmlChar *ret;
    int count = 0;

    GROW;

#ifdef DEBUG
    nbParseName++;
#endif

    /*
     * Accelerator for simple ASCII names
     */
    in = ctxt->input->cur;
    if (((*in >= 0x61) && (*in <= 0x7A)) ||
	((*in >= 0x41) && (*in <= 0x5A)) ||
	(*in == '_') || (*in == ':')) {
	in++;
	while (((*in >= 0x61) && (*in <= 0x7A)) ||
	       ((*in >= 0x41) && (*in <= 0x5A)) ||
	       ((*in >= 0x30) && (*in <= 0x39)) ||
	       (*in == '_') || (*in == '-') ||
	       (*in == ':') || (*in == '.'))
	    in++;
	if ((*in > 0) && (*in < 0x80)) {
	    count = in - ctxt->input->cur;
            if ((count > XML_MAX_NAME_LENGTH) &&
                ((ctxt->options & XML_PARSE_HUGE) == 0)) {
                xmlFatalErr(ctxt, XML_ERR_NAME_TOO_LONG, "Name");
                return(NULL);
            }
	    ret = xmlDictLookup(ctxt->dict, ctxt->input->cur, count);
	    ctxt->input->cur = in;
	    ctxt->nbChars += count;
	    ctxt->input->col += count;
	    if (ret == NULL)
	        xmlErrMemory(ctxt, NULL);
	    return(ret);
	}
    }
    /* accelerator for special cases */
    return(xmlParseNameComplex(ctxt));
}
