Fix long-standing excessive file merges Since switching to the multihead approach, we've been creating excessive file-level merges where files are marked as merged with their ancestors. This explicitly checks at commit time whether the two parent versions are linearly related, and if so, reduces the file check-in to a non-merge. Then the file is compared against the remaining parent, and, if equal, skips check-in of that file (as it's not changed). Since we're not checking in all files that were different between versions, we no longer need to mark so many files for merge. This removes most of the 'm' state marking as well. Finally, it is possible to do a tree-level merge with no file-level changes. This will happen if one user changes file A and another changes file B. Thus, if we have have two parents, we allow commit to proceed even if there are no file-level changes.

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acb14030fe0a tip
acb14030fe0a21b60322c440ad2d20cf7685a376 first
tip                                1:b9154636be938d3d431e75a7c906504a079bfe07
first                              0:acb14030fe0a21b60322c440ad2d20cf7685a376
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M a
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acb14030fe0a+ first
acb14030fe0a21b60322c440ad2d20cf7685a376+ first
M a
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c8edf04160c7+b9154636be93 tip