(cherry picked from commit 710435b5)

(cherry picked from commit 2c2e389b)

(cherry picked from commit 461cdb59)

(cherry picked from commit a87089fd)

(cherry picked from commit 1e24c2e4)

(cherry picked from commit a824c3f0)

Shutting down geth prints hundreds of annoying error messages in some
cases. The errors appear because the Stop method of eth.ProtocolManager,
miner.Miner and core.TxPool is asynchronous. Left over peer sessions
generate events which are processed after Stop even though the database
has already been closed.

The fix is to make Stop synchronous using sync.WaitGroup.

For eth.ProtocolManager, in order to make use of WaitGroup safe, we need
a way to stop new peer sessions from being added while waiting on the
WaitGroup. The eth protocol Run function now selects on a signaling
channel and adds to the WaitGroup only if ProtocolManager is not
shutting down.

For miner.worker and core.TxPool the number of goroutines is static,
WaitGroup can be used in the usual way without additional
synchronisation.

- Manager.Accounts no longer returns an error.
- Manager methods take Account instead of common.Address.
- All uses of Account with unkeyed fields are converted.

This PR introduces a 10% probability that you'll run the client with the
JIT enabled testing the new client and helps us potentially catch
errors when reported.

This feature is **disabled** for miners (disabling the JIT completely).
The JIT can however be force for miners if they enable both --jitvm and
--forcejit.

Added chain configuration options and write out during genesis database
insertion. If no "config" was found, nothing is written to the database.

Configurations are written on a per genesis base. This means
that any chain (which is identified by it's genesis hash) can have their
own chain settings.

The EVM is now initialised with an additional configured object that
allows you to turn on debugging options.

* Removed some strange code that didn't apply state reverting properly
* Refactored code setting from vm & state transition to the executioner
* Updated tests

Pending logs are now filterable through the Go API. Filter API changed
such that each filter type has it's own bucket and adding filter
explicitly requires you specify the bucket to put it in.

This removes the burden on a single object to take care of all
validation and state processing. Now instead the validation is done by
the `core.BlockValidator` (`types.Validator`) that takes care of both
header and uncle validation through the `ValidateBlock` method and state
validation through the `ValidateState` method. The state processing is
done by a new object `core.StateProcessor` (`types.Processor`) and
accepts a new state as input and uses that to process the given block's
transactions (and uncles for rewords) to calculate the state root for
the next block (P_n + 1).

There are a bunch of changes required to make this work:

- in miner: allow unregistering agents, fix RemoteAgent.Stop
- in eth/filters: make FilterSystem.Stop not crash
- in rpc/comms: move listen loop to platform-independent code

Fixes #1930. I ran the shell loop there for a few minutes and didn't see
any changes in the memory profile.

The amount of gas available for tx execution was tracked in the
StateObject representing the coinbase account. This commit makes the gas
counter a separate type in package core, which avoids unintended
consequences of intertwining the counter with state logic.

Log filtering is now using a MIPmap like approach where addresses of
logs are added to a mapped bloom bin. The current levels for the MIP are
in ranges of 1.000.000, 500.000, 100.000, 50.000, 1.000. Logs are
therefor filtered in batches of 1.000.

* Renamed ChainManager to BlockChain
* Checkpointing is no longer required and never really properly worked
when the state was corrupted.

* Moved `vm.Transfer` to `core` package and changed execution to call
`env.Transfer` instead of `core.Transfer` directly.
* core/vm: byte code VM moved to jump table instead of switch
* Moved `vm.Transfer` to `core` package and changed execution to call
  `env.Transfer` instead of `core.Transfer` directly.
* Byte code VM now shares the same code as the JITVM
* Renamed Context to Contract
* Changed initialiser of state transition & unexported methods
* Removed the Execution object and refactor `Call`, `CallCode` &
  `Create` in to their own functions instead of being methods.
* Removed the hard dep on the state for the VM. The VM now
  depends on a Database interface returned by the environment. In the
  process the core now depends less on the statedb by usage of the env
* Moved `Log` from package `core/state` to package `core/vm`.

currently, under normal circumstances, you always set the timestamp to previous.Time() + 1.
credits to https://www.reddit.com/r/ethereum/comments/3jcs5r/code_avg_block_time_vs_difficulty_adjustment/cuoi4op

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