utility: add a function to prompt user to choose a revision This patch adds a utility function to interactively prompt user to choose a revision to proceed in cases when there are multiple revisions which are candidates. The function will be used in `hg evolve`, `hg next`, `hg prev` etc. If user feedback will be good, I plan to move it to core and use it at more possible places.

tests: add a test about evolve stabilizing orphan caused by splits There are some similar tests lying around in the test suite but they are not well arranged. I wanted the test suite to be a goto reference for all the behaviors till the time we get all of them documented.

test: fix output after rev-branch-cache has been merged Mercurial core 2090044a288d added a new revbranchcache part which changed some exchange-related outputs. Glob them to ease merging with old Mercurial versions branches.

cleanup: remove duplicate import of "obsolete"

previous: fix behavior on obsolete cset when topic is involved (issue5708) This patch fixes the behavior of `hg previous` when done on an obsolete changeset having a successor of different topic. The underlying code is bit messed up, I wanted to split the topic handling to topic extension but I have postponed it to next bug.

previous: add test case when it's broken on obsolete cset This patch adds couple of tests showing `hg previous` is broken on obsolete changeset when the successor has different topic. Upcoming patch will fix this.

prev: fix the breakage of `hg previous` from obsolete cset This patch fix the breakage of `hg prev` from obsolete changeset when topic is involved. We get the topicidx of it's succesor and proceed.

prev: add a test case which shows traceback when doing prev on obsolete cset This patch adds a test which shows how `hg prev` is borken when called from a obsolete changeset and there is an active topic. The next patch will fix that.