stack: change foo#stack[:] revset to also include stack base

This makes the revset to be less "special" and it'll work like a regular slice
of a list that has all stack revs in it starting with stack base (e.g. [s0, s1,
s2, ...]).

But foo#stack revset stays the same, meaning you don't get stack base when you
use it. So if you just want to have all stack revs sans s0, you should use e.g.
foo#s instead of foo#s[:].

Note that foo#stack revset is not available on 5.3 and older versions of
Mercurial. If you cannot upgrade, you need to exclude stack base explicitly
with foo#s[1:].
8 jobs for topic/default/stack-revset in 12 minutes and 45 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Test
passed checks-py2 #251569

00:02:23

passed checks-py3 #251570

00:02:43

passed doc #251575

00:00:46

manual pytype #251568
allowed to fail manual
passed tests-py2-cext #251571

00:04:54

passed tests-py2-pure #251572

00:12:44

passed tests-py3-cext #251573

00:04:33

passed tests-py3-pure #251574

00:03:52