[MERGE] Move showing of foreign revision info onto log, for better performance.

[Ian Clatworthy]

Jelmer Vernooij wrote:
> Hi Ian,
> 
> This should improve the performance of foreign revision info displaying
> in log. For bzr.dev here it reduces the time spent on showing foreign
> revision info from 2.97 % to 0.24 %.

bb:approve

The code changes looks fine. Testing on OOo shows a drop from 50 seconds
to 45.5 seconds for 'bzr log'. Well done!

Ian C.