* cmd/evm, core/vm, internal/ethapi: Add 'err' to tracer interface CaptureEnd

* cmd/evm: fix nullpointer when there is no error

* core: remove redundant storage of transactions and receipts

* core, eth, internal: new transaction schema usage polishes

* eth: implement upgrade mechanism for db deduplication

* core, eth: drop old sequential key db upgrader

* eth: close last iterator on successful db upgrage

* core: prefix the lookup entries to make their purpose clearer

As stated in the documentation, this method should be called traceBlockFromFile
and not traceBlockByFile. Previously this would result in a 'The method ... does
not exist/is not available' error.

With this commit, core/state's access to the underlying key/value database is
mediated through an interface. Database errors are tracked in StateDB and
returned by CommitTo or the new Error method.

Motivation for this change: We can remove the light client's duplicated copy of
core/state. The light client now supports node iteration, so tracing and storage
enumeration can work with the light client (not implemented in this commit).

This prevents concurrent assignment of identical nonces when automatic
assignment is used.

More context in the bug This solves the problems of transactions being
submitted simultaneously, and getting the same nonce, due to the gap (due to
signing) between nonce-issuance and nonce-update. With this PR, a lock will
need to be acquired whenever a nonce is used, and released when the transaction
is submitted or errors out.

This commit is a preparation for the upcoming metropolis hardfork. It
prepares the state, core and vm packages such that integration with
metropolis becomes less of a hassle.

* Difficulty calculation requires header instead of individual
  parameters
* statedb.StartRecord renamed to statedb.Prepare and added Finalise
  method required by metropolis, which removes unwanted accounts from
  the state (i.e. selfdestruct)
* State keeps record of destructed objects (in addition to dirty
  objects)
* core/vm pre-compiles may now return errors
* core/vm pre-compiles gas check now take the full byte slice as argument
  instead of just the size
* core/vm now keeps several hard-fork instruction tables instead of a
  single instruction table and removes the need for hard-fork checks in
  the instructions
* core/vm contains a empty restruction function which is added in
  preparation of metropolis write-only mode operations
* Adds the bn256 curve
* Adds and sets the metropolis chain config block parameters (2^64-1)

* internal/ethapi: return empty arrays instead of null

* internal/ethapi: minor comments to avoid future regressions

Currently http cors and websocket origins are a comma separated string in the
config object. These are replaced with string arrays that are more expressive in
case of a config file.

* consensus/clique, internal/web3ext: support hash based API queries

* consensus/clique: make RPC return types public

This PR is a prototype implementation of plugable consensus engines and the
Clique PoA protocol ethereum/EIPs#225

This commit adds a build step to travis to auto-delete unstable archives older than
14 days (our regular release schedule) from Azure via ci.go purge.

The commit also pulls in the latest Azure storage code, also switching over from
the old import path (github.com/Azure/azure-sdk-for-go) to the new split one
(github.com/Azure/azure-storage-go).

This commit adds pluggable consensus engines to go-ethereum. In short, it
introduces a generic consensus interface, and refactors the entire codebase to
use this interface.

* swarm/api: fix build/tests on unsupported platforms

Skip FUSE tests if FUSE is unavailable and change build constraints so
the 'lesser' platforms aren't mentioned explicitly. The test are
compiled on all platforms to prevent regressions in _fallback.go

Also gofmt -w -s because why not.

* internal/web3ext: fix swarmfs wrappers

Remove inputFormatter specifications so users get an error
when passing the wrong number of arguments.

* swarm/api: improve FUSE-related logging and APIs

The API now returns JSON objects instead of strings.
Log messages for invalid arguments are removed.

This fixes a recent bug where 'make geth' built everything instead of
just geth.