evolve: add comptability to read old evolvestate files
When a user runs `hg evolve` with old evolve where we used to write evolvestate
the old ways i.e. without using cbor, and faces conflicts, the evolve is
interrupted. If the user updates evolve before completing the evolve, that can
result in traceback as the new evolve cannot read the old evolvestate file.
The previous patch added function to read old evolvestate file and this patch
uses that when we encounter the above mentioned case.
-------------------------
Evolve Commands Reference
-------------------------
.. 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