undo-files: cleanup backup when cleaning undos
Previously, the backups were left behind, by operation cleaning the undo's like
strip, narrow and stream clone.
The remaining elevant in the room is the transaction itself, who does not
properly cleanup undo backup before copying the new ones.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.