TravisCI and AppVeyor run the tests in very slow VMs.
Some of our tests can't cope with that. Running less tests
in parallel should make them somewhat less flakey.

State caching

This change introduces a global, per-state cache that keeps account data
in the canon state. Thanks to @karalabe for lots of fixes.

core/state: short-circuit balance change if zero value

light: fix memory expansion bug (same as fix for core/state)

ethclient: bugfix retrieving logs

core/state, light: remove unused StateObject.initCode

core/state: Fix memory expansion bug by not copying clean objects

cmd, eth: drop the blockchain version from cli/eth configs

miner: set tx index logs

rpc: format filter ID according to spec for quantities

core/types, ethclient: fix broken subscriptions

ethereum, ethclient: add SyncProgress API endpoint

cmd/evm, cmd/geth, cmd/utils: move version handling to cmd/utils

miner: Prevent attempts to close nil quit channel in agent (fixes #2948)

Transaction pool optimizations

contracts/ens: Replace setOwner with setSubnodeOwner per EIP137

swarm: plan bee for content storage and distribution on web3

Small docker run example for main README

This change imports the Swarm protocol codebase. Compared to the 'swarm'
branch, a few mostly cosmetic changes had to be made:

* The various redundant log message prefixes are gone.
* All files now have LGPLv3 license headers.
* Minor code changes were needed to please go vet and make the tests
  pass on Windows.
* Further changes were required to adapt to the go-ethereum develop
  branch and its new Go APIs.

Some code has not (yet) been brought over:

* swarm/cmd/bzzhash: will reappear as cmd/bzzhash later
* swarm/cmd/bzzup.sh: will be reimplemented in cmd/bzzup
* swarm/cmd/makegenesis: will reappear somehow
* swarm/examples/album: will move to a separate repository
* swarm/examples/filemanager: ditto
* swarm/examples/files: will not be merged
* swarm/test/*: will not be merged
* swarm/services/swear: will reappear as contracts/swear when needed