revset: fix spanset.isascending() to honor sort() or reverse() request
Because spanset.isascending() ignored the ascending flag, the result of
"fullreposet() & x" was always sorted in ascending order.
The test case is carefully chosen to call fullreposet.__and__.
Ancestors of 5
4 2 0
Ancestors of 6 and 5
3 4 2 1 0
Ancestors of 5 and 4
4 2 0
Ancestors of 7, stop at 6
6
Ancestors of 7, including revs
7 6 5 3 4 2 1 0
Ancestors of 7, 5 and 3, including revs
7 5 3 6 4 2 1 0
Descendants of 5
7 8
Descendants of 5 and 3
6 7 8
Descendants of 5 and 4
5 7 8