Replace the iter/itertext methods of Element in _elementtree with true C implementations, instead of the bootstrapped Python code. In addition to being cleaner (removing the last remains of the bootstrapping code in _elementtree), this gives a 10x performance boost for iter() on large documents.
Also reorganized the tests a bit to be more robust.
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index e068fc2..4776625 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -916,11 +916,7 @@
             _raise_serialization_error(qname)
 
     # populate qname and namespaces table
-    try:
-        iterate = elem.iter
-    except AttributeError:
-        iterate = elem.getiterator # cET compatibility
-    for elem in iterate():
+    for elem in elem.iter():
         tag = elem.tag
         if isinstance(tag, QName):
             if tag.text not in qnames: