amend: fix amending rename commit with diverged topologies (issue4405) This addresses the bug described in issue4405: when obsolescence markers are enabled, amending a commit with a file move can lead to the copy information being lost. However, the bug is more general and can be reproduced without obsmarkers as well, as demonstracted by Pierre-Yves and put into the updated test. Specifically, graph topology divergences between the filelogs and the changelog can cause copy information to be lost during amends.