commit: when committing the results of a merge, it's all or nothing
Previously, it was possible to commit just one file from a merge, which
is essentially always the wrong thing to do. This fixes issue 1049.
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
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0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
created new head
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
created new head