The original issue was that looking at all changes (action=rc all=1) the
resulting diff didn't always make sense if you clicked on the diff link.
It showed the difference between that revision and the current revision.
The PrintHtmlDiff sub was changed significantly to make it easier to
understand and to help fix this issue.
The drawback is that it now requires a new key in page and keep files:
lastmajorsummary. It goes with lastmajor and diff-major and records the
summary for that particular edit. As new changes will start recording
this new key, the change will slowly propagate in existing wikis.
Whenever you look at minor diffs, however, the existing summary key is
chosen. Plus, whenever you want to look at differences between
particular revisions, this is equivalent to looking at minor diffs. So
the only situation that is problematic is an edit history like the
following:
A - major change
B - major change (major diff, major summary, last major revision)
C - minor change
When looking at this page with diff=2, we want to show major diff, major
summary, last major revision. If B happened before this commit was
installed, the summary will be missing.
