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.

changeset:   0:acb14030fe0a
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     test

changeset:   1:863197ef0378
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     Added tag bleah for changeset acb14030fe0a21b60322c440ad2d20cf7685a376

changeset:   0:acb14030fe0a
tag:         bleah
user:        test
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     test

abort: working copy of .hgtags is changed!
(please commit .hgtags manually)
failed