Add RFile block info to validate the block was read correctly

[ctubbsii]

Ideas for this:

• Add magic number at the beginning of each RFile block, to account for empty blocks
• Add hash at the end of each RFile block to ensure the block is fully read and doesn't return early, and to ensure there aren't any errors in the block that was just read (may particularly benefit with block caching, which forces blocks to be fully read)