+ (requires downloading of the directory in the background);
+ needs more testing
+* A desired replication level can now be specified and is tracked
+ in the datastore; migration prefers content with a high
+ replication level (which decreases as replicase are created)
+ => datastore format changed; we also took out a size field
+ that was redundant, so the overall overhead remains the same
+* Peers with a full disk (or disabled migration) can now notify
+ other peers that they are not interested in migration right
+ now; as a result, less bandwidth is wasted pushing content
+ to these peers (and replication counters are not generally
+ decreased based on copies that are just discarded; naturally,
+ there is still no guarantee that the replicas will stay
+ available)