Changed version data type to signed int32

[axvm]

Fixed typo version data type in block headers. Based on issue #1413

[jonasschnelli]

ACK

References:

• https://github.com/bitcoin/bitcoin/blob/master/src/primitives/block.h#L24
• https://github.com/libbtc/libbtc/blob/master/include/btc/block.h#L45

[luke-jr]

NACK, it's a bitfield, not an integer. Implementation details are irrelevant...

[jonasschnelli]

@luke-jr: It's a bitfield when deploying SF with BIP9, but "old" blocks are still using a unsigned integer as block version. I agree that the documentation should mention the new bitfield after BIP9. But the internal type can and should be a int32 instead of a uint32.

[luke-jr]

The top bit is unusable even pre-BIP 9, so meh. :)