changelog: use headrevsfiltered
2b5940f64750 introduced use of the new filtering headrevs C implementation. It
caught TypeError to detect when to fall back to the implementation that was
compatible with old extensions. That method was however not reliable.
Instead, use the new headrevsfiltered function when passing a filter. It will
reliably fail with AttributeError when an old extension that predates
headrevsfiltered is used.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.