Fix 3-way-merge of original parent, workdir and new parent. The dirstate has to match what is in the repository (what would be checked out with 'hg update -C'), because the resulting file may be identical to the new parent, or it may be completely different. Previously the dirstate wasn't updated, so if you changed the file to look like the original parent, it might be considered unmodified relative to the new parent.

+ hg init
+ hg add a
+ hg commit -m test -d 0 0
+ hg history
changeset:   0:acb14030fe0a
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970
summary:     test

+ hg manifest
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
+ hg cat a
a
+ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions