The CommitListField now renders change description entries for the field
more similarily to its regular field view. Previously, it would just
show all old commits as removed and all new commits as added, but now it
performs a history diff between the old and new commits and renders that
instead.
The new template supports rendering commit modifications, however
commit_utils.diff_histories presently cannot generate history diffs
that contain modifications (only additions, deletions, and unmodified
entries).
