Disallow non-Namecoin tx with name outputs.

This is currently still allowed, but will be disallowed with the
upcoming fork.  It is something that isn't done by the official client
anyway.
Add block height to coinbases.  (BIP 30)

The block height in the coinbase prevents non-unique coinbase tx from
being generated.  No checks for BIP30 are done, though.
Disallow auxpow blocks that have an auxpow themselves.

This is a strange situation, but one that is currently allowed.  Forbid
it in the upcoming softfork.
Merge pull request #92 from domob1812/txversion

Fix some "strange situations" in the upcoming fork.