amend: allow aborting an `amend --patch` by saving an empty file (issue5925) This patch fixes issue5925 by allow aborting a `hg amend --patch` call by saving an empty patch file. This is similar to aborting of `hg amend` when commit message is empty. Test changes demonstrate the fix.

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