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.
Test that share-clones use the cache in the original repository.
$ . $TESTDIR/testlib/common.sh
$ hg init share-base
$ cd share-base/
$ cat >> .hg/hgrc <<EOF
> [extensions]
> evolve=
> share=
> EOF
$ hg debugbuilddag .+3:branchpoint+4*branchpoint+2
$ cd ..
$ hg --config extensions.share= share -U share-base share-client
$ cd share-client
$ hg debugupdatecache
$ test -d .hg/cache
[1]
$ test -d ../share-base/.hg/cache