A bit of a hack, but rather than handling conditional alt branches, our
dbg rbyd tree renderers just represent single-pointer alts as an alt
with both branches pointing to the place.
Unfortunately, the two branches technically have different colors. This
resulted in a bit of contention when chosing how to color the tree.
Basically Python's dict ordering would determine which color won.
Which was a bit confusing when dbgrbyd.py displayed different tree
colorings for the same rbyd. dbgrbyd.py should be idempotent!
This is solved by adding another hack to check explicitly for
same-destination branches.
Christopher Haster
37c45e1afc