[MERGE] Return BranchPushResult instance from lossy_push() and make dpush print

[Ian Clatworthy]

Jelmer Vernooij wrote:

> I've added some basic tests: one to make sure that lossy_push() raises
> LossyPushToSameVCS between normal Bazaar branches and one that checks
> the DummyForeignVCS implementation to do the right thing.

Thanks.

bb:approve

If you still want this in 1.15, be sure to co-ordinate with Bob. At a
minimum, we probably need to tweak NEWS given the API change between
1.15rc and 1.15.

Ian C.