We need unit tests that ensure that the functions of
Darcs.UI.SelectChanges do not evaluate too much of the patch sequences
they are given.
That would involve building FL's with legit patches at the beginning and
undefined's at the end.
One potential issue here is that the functions that do the interactive
selection live in IO.
We suspecct that in some cases interactive selection is reading too many
patches (see http://bugs.darcs.net/issue2436 ).