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.

pushing to ../a
searching for changes
abort: unsynced remote changes!
(did you forget to sync? use push -f to force)
pulling from ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
(run 'hg update' to get a working copy)
pushing to ../a
searching for changes
abort: push creates new remote branches!
(did you forget to merge? use push -f to force)
pushing to ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 1 changes to 1 files