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