Handle x mode bit for files and provides default mode bits for
directories.

* tests/test_upload.py:
(TestUploadMixin.assertUpPathModeEqual): New helper.
(TestUploadMixin.chmod_file): New helper.
(TestUploadMixin.test_create_file_in_subdir): Complete test.
(TestUploadMixin.test_make_file_executable): New test.

* __init__.py:
(cmd_upload.run): Cosmetic change.
(cmd_upload.upload_file): Provide mode bits depending on the
inventory executable property.
(cmd_upload.make_remote_dir): Provide defulat mode bits.
(cmd_upload.make_remote_dir_robustly): Oops, add a FIXME for the
regression.