Support rollback by restoring expansion to previous values Prevent spurious differences in the working directory after a rollback. Add tests for several rollback situations.

Do not expand at all during diff Always shrink and never expand keywords during a diff operation. Avoid user distraction e.g. because of spurious differences appearing in the commit editor.

Restore restricted read mode value after overwriting Even though just enforcing expansion after overwriting files in the working directory caused no problems that we know of, this avoids a potential source of problems (e.g. in collaboration other extensions) at no costs.