Depend on elementtree 1.2.6.

setup.py

@@ -76,7 +76,7 @@ dist = setup(
                           'CHANGES.txt', 'TODO.txt', 'LICENSES.txt',
                           'COPYRIGHT.txt'])],
     install_requires = ['medusa >= 0.5.4', 'meld3 >= 0.6.3',
-                        'elementtree >= 1.2.6'],
+                        'elementtree >= 1.2.6,<1.2.7'],
     extras_require = {'iterparse':['cElementTree >= 1.0.2']},
     include_package_data = True,
     zip_safe = False,