tests/test-commit-copy.t

revsets: let parents() return parents of working dir

This patch makes the 'set' argument to revset function parents() optional.
Like p1() and p2(), if no argument is given, returns the parent(s) of the
working directory.

Morally equivalent to 'p1()+p2()', as expected.

  $ hg init dir
  $ cd dir
  $ echo bleh > bar
  $ hg add bar
  $ hg ci -m 'add bar'

  $ hg cp bar foo
  $ echo >> bar
  $ hg ci -m 'cp bar foo; change bar'

  $ hg debugrename foo
  foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
  $ hg debugindex .hg/store/data/bar.i
     rev    offset  length   base linkrev nodeid       p1           p2
       0         0       6      0       0 26d3ca0dfd18 000000000000 000000000000
       1         6       7      1       1 d267bddd54f7 26d3ca0dfd18 000000000000