'Add foldername entry for an account.'

def addAccountFolder(self, accountname, folder_root, foldername):

    if (accountname not in self._intermediates):
        self._intermediates[accountname] = _IntermediateMbnames(accountname, folder_root, self._mbnamesdir, self._folderfilter, self._dryrun, self.ui)
    self._intermediates[accountname].add(foldername)
