rebase: rewrite _computeobsoletenotrebased...
rebase: rewrite _computeobsoletenotrebased
The old code stores successors of all related nodes together, which works
fine if destination is unique. A future patch would make destination
non-unique so let's change the implementation to test successors for
rebaseset separately.
Differential Revision:
https://phab.mercurial-scm.org/D347