copies: avoid unwanted side effect from one branch to another...
copies: avoid unwanted side effect from one branch to another
Without this copy, change in a one descendant branch (With "remove" change
only) could affect computation on another descendant branches.
This was not caugh by the test because the test graph are "too simple". I
started writing more test in that regards, but I a submitting this changes
earlier because I want to get more code landed to allow other optimisation work
to happens.
Differential Revision:
https://phab.mercurial-scm.org/D9416
