RFC: remove traceback from "newer branch format than your bzr"

[James Westby]

Martin Pool wrote:
> How about if we said something like this
> 
> $ bzr branch....
> AbsentContentFactory has no attribute...
> This probably indicates a bug in Bazaar.  Sorry.  For help or to
> report a bug see http://bazaar-......

That's an improvement. Perhaps it should also point to wherever
.bzr.log is as we would want people to include the relevant parts of
that in their bug report.

Thanks,

James