So, as we discussed today, I've seen mention of the following ideas of
how we can do it:
1. introduce a "fall-back POTMsgSet" where we basically tag matching
POTMsgSets between Ubuntu and upstream
2. re-use and fix is_imported flag to finally be is_upstream flag as it
should have been from the start, making use of existing message sharing
3. do an actual import from upstream translations into Ubuntu
4. cleverly extend message-sharing to support this another dimension of
the problem
5. handle it at updateTranslation level: negotiate what action needs to
be taken in code, and do merging and duplication as necessary
2 and 4 would be more scalable (i.e. wouldn't grow the DB too much), 1
is close to that, yet 3 and 5 would be very much unscalable. To top it
off, 3 would be the only one with only a one-way sync, which I think
scratches it off the list.
