On FC8, the config is originating in /etc/mercurial/hgrc.d/mergetools.rc. The
problem is that the configuration for filemerge is completely inappropriate.

It seems to me that a bad mergetools.rc should not be installed unless the
packager really works to break the packaging. Renaming mergetools.rc to
mergetools.rc.sample seems like a good step, but it also seems like a good idea
to find some way for the default installation to work out of the box with
minimal packager intervention.

Might it make sense to ship multiple mergetool.rc samples, one for each major
platform?