Renamed xml dir to xml_templates.

This avoids an import warning on Python 2.7:

```
Products/PluggableAuthService/plugins/exportimport.py:19:
ImportWarning: Not importing directory '.../PluggableAuthService/plugins/xml': missing __init__.py
  from xml.dom.minidom import parseString
```

CHANGES.rst

@@ -4,6 +4,9 @@ Change Log
 2.5 (unreleased)
 ----------------
 
+- Renamed ``xml`` dir to ``xml_templates``.
+  This avoids an import warning on Python 2.7.
+
 - Disable ZMI CSRF check and log it if sessioning is not available
   instead of breaking ZMI interactions
 

Products/PluggableAuthService/plugins/exportimport.py

@@ -61,7 +61,7 @@ def export(self, export_context, subdir, root=False):
         """ See IFilesystemExporter.
         """
         package_path = getPackagePath(self)
-        template = PageTemplateFile('xml/%s' % self._FILENAME,
+        template = PageTemplateFile('xml_templates/%s' % self._FILENAME,
                                     package_path).__of__(self.context)
         info = self._getExportInfo()
         export_context.writeDataFile('%s.xml' % self.context.getId(),