If 'readonly' is True, folders shouldn't be created (regardless of
'createfolders' option). With old behavior, instead folders were always created
when 'readonly' is True (even if 'createfolders' was also False), which is a
serious bug (offlineimap was creating folders in all read-only repositories).
'createfolders' should only play a role if 'readonly' is False, in which case
folders should only be created if 'createfolders' is True.
Submitted-by: Vladimir Nesov <robotact@gmail.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>