tests/test-nested-repo.t

tests: avoid referring to pvec in demandimport test

Nothing else currently uses pvec, so we may want to delete it (but
Augie Fackler says he may want to use it). To enable deletion, this
patch replaces it by the error module in the demandimport test (any
module works). However, since the error module had already been loaded
at this point in the test (via the util module), I moved it earlier in
the test so it's still not loaded (although I'm not sure if that's
even relevant to the test).

Differential Revision: https://phab.mercurial-scm.org/D2287

  $ hg init a
  $ cd a
  $ hg init b
  $ echo x > b/x

Should print nothing:

  $ hg add b
  $ hg st

  $ echo y > b/y
  $ hg st

Should fail:

  $ hg st b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]
  $ hg add b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]

Should fail:

  $ hg add b b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]
  $ hg st

Should arguably print nothing:

  $ hg st b

  $ echo a > a
  $ hg ci -Ama a

Should fail:

  $ hg mv a b
  abort: path 'b/a' is inside nested repo 'b'
  [255]
  $ hg st

  $ cd ..