Add ElementPath to the list of package ignored by demand import

The bzrlib try to import the ElementPath module but had a fallback in
case the import fails. Lazy import of this module leads to later
failure.

The bzrlib is used by the convert extension.

hgext/convert/bzr.py

@@ -14,6 +14,7 b' from mercurial import demandimport'
 demandimport.ignore.extend([
         'bzrlib.transactions',
         'bzrlib.urlutils',
+        'ElementPath',
     ])
 
 from mercurial.i18n import _