patch.diff: restrict matcher to relative root in certain cases
Previously we'd request all results, then filter by relative root. This is
clearly inefficient, so we now restrict the matcher to the relative root for
certain easy cases.
The particular case here is when the matcher matches all files. In that case we
can simply create a matcher by the relative root.
This is purely an optimization and has no impact on correctness.
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