tests/test-status-eacces.t

dirstate-v2: add check of parent/child nodes being related when writing

This stems from a corruption seen in a private repository. We're not sure
of the source of the corruption, and it's very possible that we're seeing
compounded effects of multiple writes on a corrupted dirstate.

Adding this check is not expensive in itself and large writes of the dirstate
are not common.

This change does not catch this problem at the root node, the next one will.

#testcases dirstate-v1 dirstate-v2

#if dirstate-v2
  $ cat >> $HGRCPATH << EOF
  > [format]
  > use-dirstate-v2=1
  > [storage]
  > dirstate-v2.slow-path=allow
  > EOF
#endif


The proliferation of status implementations can be confusing:
- The pure python implementation:
(no-rhg pure !)
- The C implementation:
(no-rhg no-rust no-pure !)
- The two rust implementations:
(rhg !)
(no-rhg rust !)

  $ hg init repo1
  $ cd repo1
  $ mkdir d1
  $ touch d1/x
  $ hg commit -Am.
  adding d1/x
  $ touch d1/y
  $ chmod -r d1
  $ hg status
  d1: $EACCES$
  ! d1/x (rhg !)
  ! d1/x (no-rhg rust !)
  $ hg status
  d1: $EACCES$
  ! d1/x (rust !)
  ! d1/x (no-rust rhg !)
  $ chmod +r d1
  $ hg status
  ? d1/y

  $ touch d1/z
  $ hg status
  ? d1/y
  ? d1/z