Description:
------------
xmlwriter_write_dtd_entity() creates attlist, not entity.

Proposed patch: 
http://home.oslo.nith.no/~maghan/xmlwriter_write_dtd_entity.patch.txt

Reproduce code:
---------------
<?php
$xw = xmlwriter_open_memory();
xmlwriter_start_document($xw, NULL, "UTF-8");
xmlwriter_write_dtd_entity($xw, "ent2", "val2");
xmlwriter_end_document($xw);
print xmlwriter_flush($xw, true);
?>


Expected result:
----------------
<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY ent2 "val2">

Actual result:
--------------
<?xml version="1.0" encoding="UTF-8"?>
<!ATTLIST ent2 val2>