statecheck: added support for STATES
This removes `STATES` from `state.py` and adds support to
`statecheck` class to handle its features.
`getrepostate()` function is modified accordingly.
This adds a method 'cmdutil.addunfinished()' for appending to
the unfinishedstate list so as to keep 'merge' and 'bisect' at the last.
This also makes two separate message formats for `checkunfinished()` and
`getrepostate()` as there were previously present.
Results of test changed are shown.
Differential Revision: https://phab.mercurial-scm.org/D6503
#require docutils gettext
$ $TESTDIR/check-gendoc ru
checking for parse errors