hgweb: use patch.diff() to make sensible diffs (
issue1223,
issue1258)
This gets us git diffs when enabled and doesn't pick erratic file parents.
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
created new head
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)