Medium: PE: Revert group stickiness to the 'old way'
Resources don't all have the same score, but for member M of a group with size N,
its score will be (N-M)*stickiness - since member M inherits the preference of the
members that come after it in the group via the colocation constraints.

Mercurial revision: aeaf9d8fff5370e0bd75743ed9ee6a4470e52a1f