Update afl_rev_id even if the edit summary changed

(bug 28633) With $wgUseAutomaticEditSummaries=true, the edit summary is
different between EditFilterMerged and ArticleSaveComplete. AbuseFilter
was using edit summary changes to attempt to detect whether the two
hooks refer to the same edit. If it really is possible for multiple
edits to be performed in the same request, with arbitrary patterns of
EditFilterMerged and ArticleSaveComplete calls, then some more robust
method would be needed to match the hook calls. But I don't think that
is necessary at present.

Change-Id: I94321905f38eafde8add00eff73745af255c1f15