stack: use stack._revs instead of stack.revs[1:] in external children revset
The revset in question excludes all revs that are part of the stack. Using
stack.revs[1:] works (rev #0 is stack base, which is not a part of the stack),
but using stack._revs is technically more correct, because this variable is
specifically designed to hold only revisions that are part of the stack.
#require test-repo
$ checkflake8() {
> if ! (which flake8 > /dev/null); then
> echo skipped: missing tool: flake8;
> exit 80;
> fi;
> };
$ checkflake8
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run flake8 if it exists; if it doesn't, then just skip
$ hg files -0 'set:(**.py or grep("^#!.*python")) - removed()' \
> -X hgext3rd/evolve/thirdparty \
> 2>/dev/null \
> | xargs -0 flake8