tests/test-purge-ignored-directory.t

rhg: ignore readonly FS error when saving dirstate

The error is already ignored when the .hg directory is read-only,
so this is only fair. (the python hg is silent on readonly fs, too)

skip ignored directories if -i or --all not specified

  $ hg init t
  $ cd t
  $ echo 'ignored' > .hgignore
  $ hg ci -qA -m init -d'2 0'
  $ mkdir ignored
  $ ls
  ignored
  $ hg purge -v --no-confirm
  $ ls
  ignored