Made caches dataset-aware so that they won't cyclically evict partitions

core/src/main/scala/spark/BoundedMemoryCache.scala

core/src/main/scala/spark/Cache.scala

core/src/main/scala/spark/CacheTracker.scala

core/src/main/scala/spark/DiskSpillingCache.scala

core/src/main/scala/spark/SerializingCache.scala

core/src/main/scala/spark/SoftReferenceCache.scala

core/src/main/scala/spark/WeakReferenceCache.scala

.../src/main/scala/spark/broadcast/BitTorrentBroadcast.scala

core/src/main/scala/spark/broadcast/ChainedBroadcast.scala

core/src/main/scala/spark/broadcast/DfsBroadcast.scala

core/src/main/scala/spark/broadcast/TreeBroadcast.scala