Merge branch 'en/ancestry-path-in-a-range'

Merge branch 'en/ancestry-path-in-a-range'

"git rev-list --ancestry-path=C A..B" is a natural extension of
"git rev-list A..B"; instead of choosing a subset of A..B to those
that have ancestry relationship with A, it lets a subset with
ancestry relationship with C.

* en/ancestry-path-in-a-range:
  revision: allow --ancestry-path to take an argument
  t6019: modernize tests with helper
  rev-list-options.txt: fix simple typo