log: add config for making `hg log -G` always topo-sorted

Authored by martinvonz.


log: add config for making hg log -G always topo-sorted

I (and everyone else at Google) have an log alias that adds graph mode
and templating. I have another one that builds on the first and also
restricts the set of revisions to only show those I'm most likely to
care about. This second alias also adds topological sorting. I still
sometimes use the first one. When I do, it very often bothers me that
it's not topologically sorted (branches are interleaved). This patch
adds a config option for always using topological sorting with graph

The revision set is sorted eagerly, which seems like a bad idea, but
it doesn't seem to make a big difference in the hg repo (150ms). I
initially tried to instead wrap the user's revset in sort(...,topo),
but that seemed much harder.

Differential Revision: https://phab.mercurial-scm.org/D6331