revset: make children() not look at p2 if null (issue5439)
Unlike p1 = null, p2 = null denotes the revision has only one parent, which
shouldn't be considered a child of the null revision. This was spotted while
fixing the issue4682 and rediscovered as issue5439.
setup: pass named argument to setup_zstd
The next release from upstream adds another named argument to this
function. Specify arguments by name so there is no ambiguity about
which argument is being passed.