tests: add more complete test for status changes on amend This demonstrates that missing/untracked files are handled incorrectly. The correct outputs are suppressed by (false !), and wrong outputs are added with (true !) instead. The setup code is copied from test-status-rev.t.

# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)