Added back coarse-grained Mesos scheduler based on StandaloneScheduler.

core/src/main/scala/spark/SparkContext.scala

...main/scala/spark/executor/StandaloneExecutorBackend.scala

...main/scala/spark/scheduler/cluster/ClusterScheduler.scala

...la/spark/scheduler/cluster/StandaloneClusterMessage.scala

.../spark/scheduler/cluster/StandaloneSchedulerBackend.scala

.../main/scala/spark/scheduler/cluster/TaskDescription.scala

...c/main/scala/spark/scheduler/cluster/TaskSetManager.scala

...in/scala/spark/scheduler/mesos/CoarseMesosScheduler.scala

...a/spark/scheduler/mesos/CoarseMesosSchedulerBackend.scala

...n/scala/spark/scheduler/mesos/MesosSchedulerBackend.scala

core/src/main/scala/spark/util/SerializableBuffer.scala