[merge] fetch progress improvements

[Robert Collins]

Robert Collins has voted tweak.
Status is now: Conditionally approved
Comment:
Looks good. Can we please keep the mutter about fetching, its a very 
useful debugging tool in bzrlib.log. The reduction in roundtrips is very 
unlikely to be generators, rather its likely one less call to a 
repository somewhere. Diffing the hpss calls can tell you very easily if 
you are interested.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3Ce01316480903120208j612cc238nec2fbae8e42e1375%40mail.gmail.com%3E
Project: Bazaar