rem: CachedBlock(Volume *volume, block_run run, bool empty = false) : fVolume(volume), fBlock(NULL) { SetTo(volume->ToBlock(run), empty); }
add: CachedBlock::CachedBlock(CachedBlock *cached) : fVolume(cached->fVolume), fBlock(cached->fBlock), fBlockNumber(cached->BlockNumber()) { cached->Keep(); }
context: 		CachedBlock(Volume *volume, block_run run, bool empty = false)			:			fVolume(volume),			fBlock(NULL)		{			SetTo(volume->ToBlock(run), empty);		}