stack: allow to refer to changeset using "t2" form hg up "t0" is seen as "update to the first changeset of my current topic". Eventually we'll drop the "t2" form in favor of the planned generic indexing operator '.{t2}'.

topic: don't take topic into account when pushing to non-topic repo Previously, pushing to a non-publishing repository without topic support would wrongfully use topic when searching for new heads.