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

[Stephen J. Turnbull]

I withdraw my previous post in favor of Russel Winder's much more
coherent and accurate expression of basically the same ideas.

Just for context:

Stephen J. Turnbull writes:
 > Martin Pool writes:
 > 
 >  > $ bzr branch....
 >  > AbsentContentFactory has no attribute...
 >  > This probably indicates a bug in Bazaar.  Sorry.  For help or to
 >  > report a bug see http://bazaar-......
 > 
 > Urk.  Now you are going to get a bug report

[etc, etc]