tests/test-issue1438.t

import-checker.py: exit with code 0 if no error is detected

Before this patch, `import-checker.py` exits with non-0 code, if no
error is detected. This is unusual as Unix command.

This change may be a one of preparations for issue4677, because this
can avoid extra explanation about unusual exit code of
`import-checker.py` for third party tool developers.

#require symlink

http://mercurial.selenic.com/bts/issue1438

  $ hg init

  $ ln -s foo link
  $ hg add link
  $ hg ci -mbad link
  $ hg rm link
  $ hg ci -mok
  $ hg diff -g -r 0:1 > bad.patch

  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg import --no-commit bad.patch
  applying bad.patch

  $ hg status
  R link
  ? bad.patch