context: implement mergestate() method
This will let us have the mergestate storage be controlled by the context. In
particular, for working contexts we should use the existing mergestate, but
for overlay contexts it's inappropriate to drop files in .hg/merge.
Differential Revision: https://phab.mercurial-scm.org/D8551
%include map-cmdline.default
[templates]
changeset = '{cset}{lbisect}{branches}{bookmarks}{tags}{parents}{luser}{ldate}{summary}\n'
changeset_quiet = '{lshortbisect} {rev}:{node|short}\n'
changeset_verbose = '{cset}{lbisect}{branches}{bookmarks}{tags}{parents}{luser}{ldate}{lfiles}{lfile_copies_switch}{description}\n'
changeset_debug = '{fullcset}{lbisect}{branches}{bookmarks}{tags}{lphase}{parents}{manifest}{luser}{ldate}{lfile_mods}{lfile_adds}{lfile_dels}{lfile_copies_switch}{extras}{description}\n'
# We take the zeroth word in order to omit "(implicit)" in the label
bisectlabel = ' bisect.{word('0', bisect)}'
lbisect ='{label("log.bisect{if(bisect, bisectlabel)}",
"bisect: {bisect}\n")}'
lshortbisect ='{label("log.bisect{if(bisect, bisectlabel)}",
"{bisect|shortbisect}")}'