commit: force create a new filenode if it was set in mergestate by merge
For reasons mentioned in previous commits, we will like to forcefully create a
new filenode sometimes.
Combination of this patch and previous one, we fixed a case in
`test-merge-combination.t`.
This does not yet results in conflict where it should, I need to investigate
more about what's happening as it should be a change-delete conflict now.
Differential Revision: https://phab.mercurial-scm.org/D8989
== Local
Ready.
Un and Deux
Eins und Zwei
One and Two
Eins und Zwei
Uno und Due
== Remote
Ready.
REQ: foo?one=Vo&two=Efvy
-> Vo!boe!Efvy
Un and Deux
REQ: bar?b=Fjot&a=[xfj
-> Fjot!voe![xfj
Eins und Zwei
REQ: batch?cmds=foo:one=Pof,two=Uxp;bar:b=Fjot,a=[xfj;bar:b=Vop,a=Evf
-> Pof!boe!Uxp;Fjot!voe![xfj;Vop!voe!Evf
One and Two
Eins und Zwei
Uno und Due