Podcast feed update status fixes
- podcast: make feed status 'updating' as transient status
This is primarily needed for handling feed update cancellations during
rhythmbox close, as there is no definite timeline from plparser on how
quickly it will detect the cancellation and invoke the user
callback. So, rather than waiting / blocking for plparser callback
during rhythmbox close, we make the feed 'updating' status as
transient.
- podcast: update feed status on feed update cancellation