reachableroots: sort the smartset in the pure version too
Changeset be8a4e0800d8 uses smartset lazy sorting for the C version. We need to
apply the same to the pure version for consistency. This is fixing the tests
with --pure.
http://mercurial.selenic.com/bts/issue1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..