sparse-revlog: skip the span check in the sparse-revlog case
This significantly improves the performance on unbundling on smaller
repositories.
Mercurial: unbundling 1K revisions
no-sparse-revlog: 500 ms
sparse-revlog-before: 689 ms
sparse-revlog-after: 484 ms
Pypy: unbundling 1K revisions
no-sparse-revlog: 1.242 s
sparse-revlog-before: 1.135 s
sparse-revlog-after: 0.860 s
NetBeans: unbundling 1K revisions
no-sparse-revlog: 1.386 s
sparse-revlog-before: 2.368 s
sparse-revlog-after: 1.191 s
Mozilla: unbundling 1K revisions
no-sparse-revlog: 3.103 s
sparse-revlog-before: 3.367 s
sparse-revlog-after: 3.093 s
Ancestors of 5
4 2 0
Ancestors of 6 and 5
4 3 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 4 3 2 1 0
Ancestors of 7, 5 and 3, including revs
7 6 5 4 3 2 1 0
Descendants of 5
7 8
Descendants of 5 and 3
6 7 8
Descendants of 5 and 4
5 7 8