context: introduce merge.preferancestor for controlling which ancestor to pick
Multiple revisions can be specified in merge.preferancestor, separated by
whitespace. First match wins.
This makes it possible to overrule the default of picking the common ancestor
with the lowest hash value among the "best" (introduced in
3605d4e7e618).
This can for instance help with some merges where the 'wrong' ancestor is used.
There will thus be some overlap between this and the problems that can be
solved with a future 'consensus merge'.
Mercurial will show a note like
note: using
40663881a6dd as ancestor of
3b08d01b0ab5 and
adfe50279922
alternatively, use --config merge.preferancestor=
0f6b37dbe527
when the option is available, listing all the alternative ancestors.