Make mbnames to work with intermediate files, one per account, in the JSON
format. The mbnames target is built from those intermediate files.
Github-Fix: https://github.com/OfflineIMAP/offlineimap/issues/66
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
This eases testing of option values inside the code. This instance
is implemented as the read-only copy of the obtained 'options' object,
so callers won't be able to modify its contents.
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>