Not all Datastructures are updated when a block is deleted

Currently when a block is deleted, DataNode just deletes the physical file and updates its map. We need to update more things. For e.g. numBlocks in FSDir is not decremented.. effect of this would be that we will create more subdirectories than necessary. It might not show up badly yet since numBlocks gets correct value when the dataNode restarts. I have to see what else needs to be updated.