prev: jump to parent's successor if parent is obsolete and topic is involved `hg stack` shows a linear chain of commits even when they are not linear chain and some changesets are obsoleted and have successors as separate head. This is very nice to have a post evolution view of the stack. However when `hg prev` is run on an unstable changeset whose parent is obsolete and does not topic but parents successor has the topic, it shows no parent on the topic. This patch makes `hg prev` update to parent's successor and make things follow the stack order.

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Evolve Commands Reference
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.. highlight:: none

amend
-----

.. hghelp:: amend

evolve
------

.. hghelp:: evolve

fold
----

.. hghelp:: fold

metaedit
--------

.. hghelp:: metaedit

next
----

.. hghelp:: next

obslog
------

.. hghelp:: obslog

pdiff
-----

.. hghelp:: pdiff

previous
--------

.. hghelp:: previous

prune
-----

.. hghelp:: prune

pstatus
-------

.. hghelp:: pstatus

split
-----

.. hghelp:: split

touch
-----

.. hghelp:: touch

uncommit
--------

.. hghelp:: uncommit