branch heads: fix regression introduced in e67e5b60e55f (issue1726)
For merge nodes it is not adequate to only check a single possible
branch head for whether it is an ancestor of the latest head, but it
needs to be done for each possible branch head.
default = 'changelog'
feedupdated = '<updated>{date|rfc3339date}</updated>'
mimetype = 'application/atom+xml; charset={encoding}'
header = header.tmpl
changelog = changelog.tmpl
changelogentry = changelogentry.tmpl
filelog = filelog.tmpl
filelogentry = filelogentry.tmpl
tags = tags.tmpl
tagentry = tagentry.tmpl
error = error.tmpl