update: calculate 'partial' as core does

discovery: flake8

destination: flake8

style: update __init__.py

compat: adapt to the new destspace argument of destmerge The argument is currently ignored in the topic case for simplicity, but we properly accept it and propagate it to the original function to prevent crash and behavior regression in the non-topic case.

stack: prevent crash when topic is rooted on nullid We exclude null from displayed base. This was causing a crash when trying to display its description (we'll still have to handle the empty description case, but it is now less urgent).

test: add topic on the first 2 changesets too This will be used to add a test for topic rooted on nullid. We introduce this in its own changeset to reduce the noise if the actual changeset.

test: remove comment about new head warning The new head warning was buggy. This was fixed in bdc5bb223b50.

stack: also change the indexing of the t# reference Changeset 61f36480740f changed the index displayed (we now index from 1), but forgot to update the logic used to resolve the 't#' name. This changeset fixes it.

stack: change the ascii symbold for base Now that the children line go upward, '_' is no longer clear as is take the lower part of the line. We go for '^' that use the upper part.