tests/test-run-tests.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.

Simple commands:

  $ echo foo
  foo
  $ printf 'bar\nbaz\n' | cat
  bar
  baz

Multi-line command:

  $ foo() {
  >     echo bar
  > }
  $ foo
  bar

Regular expressions:

  $ echo foobarbaz
  foobar.* (re)
  $ echo barbazquux
  .*quux.* (re)

Globs:

  $ printf '* \\foobarbaz {10}\n'
  \* \\fo?bar* {10} (glob)

Literal match ending in " (re)":

  $ echo 'foo (re)'
  foo (re)

Exit code:

  $ (exit 1) 
  [1]