SEC-10 Uncle validation does not include all parts of block header validity function

See Yellow Paper section 11.1 "Uncle Validation". Part of validation of an uncle is the block header validity function (V). Only the PoW nonce check from V is currently implemented.

Uncle validation code: https://github.com/ethereum/go-ethereum/blob/develop/core/block_processor.go#L280

**STATUS: OPEN**
