[MERGE] Fetch into stacked branches works correctly

[Martin Pool]

Martin Pool has voted approve.
Status is now: Approved
Comment:
Since the fix is to just InterPackRepository, it makes me wonder if we 
should actually be testing this in a place that will cover more 
different InterRepository situations.  At the moment I think this test 
will only run in the case of a Branch7 stacked on top of another Branch7 
with the default repository type.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C488D6605.9050500%40aaronbentley.com%3E