rem: CachedBlock::SetTo(off_t block, bool empty)
add: CachedBlock::SetTo(block_run run, bool empty)
context: CachedBlock::SetTo(off_t block, bool empty){	Unset();	fBlockNumber = block;	return fBlock = empty ? (uint8 *)get_empty_block(fVolume->Device(), block, BlockSize())						  : (uint8 *)get_block(fVolume->Device(), block, BlockSize());}