cmd/core,xeth: removed unneeded states & added batch writes

all: license fixes

cmd, core, eth, ethdb: cache flag to allocate memory for db internal use

core: fix an RLP encoding data race due to deep struct copy

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

crypto/curve.go is not our code and has its own license. This commit
excludes it in update-license.go and removes our GPL header.

accounts: fix data race when key is locked after the unlock timeout

Legalese updates

miner: fix current work data race

Fixed canary to require 2+ nonzero, not sum 2+

While here, also improve the docs and speed up the tests.
The tests used the scrypt keystore with ridiculous settins and took 20s
each.

xeth: fix #1485, data race in fiilter creation and event firing

cmd/ethtest, tests: add support for RLP JSON tests

miner: moved state sync

Travis container support

Decoding did not reject byte arrays of length one with a single element
b where 55 < b < 128. Such byte arrays must be rejected because
they must be encoded as the single byte b instead.

Moved the state sync so it only syncs the state when the block mining yield a possitive result

Prompt user to accept legalese when datadir doesn't exist

miner: smart mining

xeth: removed mutex lock

core: during chain reorg rewrite receipts and transactions

Work is now handled and carried over multiple sessions. Previously one
session only was assumed, potentially resulting in invalid (outdated)
work

* Larger work / result queue
* Full validation option