init: cache repo.topics

stack: add warning about multiple heads This seems a good spot to nudge people toward reducing there head count.

stack: add some behind information This is the next useful thing after branch

stack: add some basic branch information In the same spirit as knowing the topic you are on, having some branch data seem useful (yet, this smell a bit like summary)

stack: add some header with the topic name This is the first step of a move to add more data about a stack in the command output.

test: add testing of stack output in 'stack-data' test. We are going to display common information, so we reuse test case.

test: rename 'list' test to 'stack-data' We are about to add stack data information to 'hg stack'. As we'll re-use the test data creating the 'test-topic-list.t' we need to rename it first to embrace its new semantic.

stack: also dim bases Now that they may have index it seems better to have a stronger marking for bases.

stack: reusing the index number in base when applicable This clarify the branching when it is easy to track back the branching point. This does not takes the evolution graph into account yet.

stack: extra argument validation logic outside of showstack It seems sensible keep the 'showstack' function purely about actually displaying and existing stack.

summary: properly label the topic name in summary This should be labelled 'topic.active' so that color can pick it up properly.

topic: list the branches this topic belong to when verbose Using the verbose listing a bit more, this seems to be useful information.

topic: properly justify the verbose data when listing topic We align all data to the widest topic.

ngtip: rely on topicmap for 'ngtip' ngtip is an old function that predates the introduction of a more proper topic aware 'topicmap'. We replace the old code with a call to the new one. This change set function return type and have minor effect in a couple of place.

topic: list the number of 'behind' changeset when --verbose is used Displaying more information in the topic list is useful, we continue with the number of 'behind' changesets. This 'behind' count the number of new changesets on the default rebase destination. This will highlight topics that need rebasing.