revset: add ^ and ~ operators from parentrevspec extension ^ (Nth parent) and ~ (Nth first ancestor) are infix operators that match certain ancestors of the set: set^0 the set set^1 (also available as set^) the first parent of every changeset in set set^2 the second parent of every changeset in set set~0 the set set~1 the first ancestor (i.e. the first parent) of every changeset in set set~2 the second ancestor (i.e. first parent of first parent) of every changeset in set set~N the Nth ancestor (following first parents only) of every changeset in set; set~N is equivalent to set^1^1..., with ^1 repeated N times.