progress: document progress.debug config option
I think it was not spotted by test-check-config.t that we had not
documented it because no caller refers to the ui object simply as "ui"
(it was either "self.ui" or just "self").
Differential Revision: https://phab.mercurial-scm.org/D5526
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