py3: source-transform only call-sites of iteritems(), not definitions branchmap.branchcache, among other classes, defines a iteritems(). That currently gets replaced by items() by the source transformer. That makes it harder for extensions to work with both py2 and py3, since they have to call either items() or iteritems() on branchcache. Let's not replace definitions of iteritems() (and itervalues()) and only replace the call-sites. We need to also add an items() alias to branchcache (etc) so our transformer call-sites will find it. Differential Revision: https://phab.mercurial-scm.org/D6641