Added a `Difference` method to `types.Transactions` which sets the
receiver to the difference of a to b (NOTE: not a **and** b).

Transaction pool subscribes to RemovedTransactionEvent adding back to
those potential missing from the chain.

When a chain re-org occurs remove any transactions that were removed
from the canonical chain during the re-org as well as the receipts that
were generated in the process.

Closes #1746

I forgot to update one instance of "go-ethereum" in commit 3f047be5.

All code outside of cmd/ is licensed as LGPL. The headers
now reflect this by calling the whole work "the go-ethereum library".

Implemented the --genesis flag thru which we can set a custom genesis
block, including the official Ethereum genesis block.

* Update => SyncIntermediate
* Added SyncObjects

SyncIntermediate only updates whatever has changed, but, as a side
effect, requires much more disk space.

SyncObjects will only sync whatever is required for a block and will not
save intermediate state to disk. As drawback this requires more time
when more txs come in.

You can set the nonce of the block with `--genesisnonce`. When the
genesis nonce changes and it doesn't match with the first block in your
database it will fail. A new `datadir` must be given if the nonce of the
genesis block changes.

* miner control moved to `admin.miner`
* miner option to set extra data
* block extra now bytes

* Add params package with exported variables generated from
  github.com/ethereum/common/blob/master/params.json
* Use params package variables in applicable places
* Add check for minimum gas limit in validation of block's gas limit
* Remove common/params.json from go-ethereum to avoid
  outdated version of it

* Added new CreateAccount method which properly overwrites previous
  accounts (excluding balance)
* Fixed block tests (100% success)