/brz/remove-bazaar

Handle deletions. Robust implementation.

* test_upload.py:
(TestIncrementalUpload.test_delete_dir_and_subdir,
TestIncrementalUpload.test_delete_one_file_rename_to_deleted,
TestIncrementalUpload.test_rename_outside_dir_delete_dir): Make
the trivial deletion fails.

* __init__.py:
Use lazy_import.
(cmd_upload.delete_remote_file, cmd_upload.delete_remote_dir,
cmd_upload.delete_remote_dir_maybe, cmd_upload.finish_deletions):
Better deletion handling.
(cmd_upload.upload_tree): Handle dir deletions.