ALLOW_OVERLAPPING

by default, creating a checkpoint fails if there are already existing checkoints that reference the same devices.

With this flag, creation of such checkpoints is allowed, however, if an older checkpoint that references overlapping devices gets rolled back, it will automatically destroy this checkpoint during rollback. This allows to create several overlapping checkpoints in parallel, and rollback to them at will. With the special case that rolling back to an older checkpoint will invalidate all overlapping younger checkpoints. This opts-in that the checkpoint can be automatically destroyed by the rollback of an older checkpoint. Since: 1.12.