ValidateFields was introduced before the rlp decoder disallowed nil
values. Decoding RLP will never return nil values, there is no need
to check for them.

internal/ethapi: Fix bug in opCodeWrapper usage

internal/ethapi: Improve tracer error reporting and serialization

core/vm, eth: Add support for javascript trace functions

cmd/utils: removed DAO oppose / support message

cmd/geth: added copyright and license information

core: Refactor tracing to make Tracer the main interface

As per GNU GPL requirement I've added the copyright and the license
information as a subcommand as well as a copyright notice when
displaying the help command.

This CL makes several refactors:
 - Define a Tracer interface, implementing the `CaptureState` method
 - Add the VM environment as the first argument of
   `Tracer.CaptureState`
 - Rename existing functionality `StructLogger` an make it an
   implementation of `Tracer`
 - Delete `StructLogCollector` and make `StructLogger` collect the logs
   directly
 - Change all callers to use the new `StructLogger` where necessary and
   extract logs from that.
 - Deletes the apparently obsolete and likely nonfunctional 'TraceCall'
   from the eth API.

Callers that only wish accumulated logs can use the `StructLogger`
implementation straightforwardly. Callers that wish to efficiently
capture VM traces and operate on them without excessive copying can now
implement the `Tracer` interface to receive VM state at each step and
do with it as they wish.

This CL also removes the accumulation of logs from the vm.Environment;
this was necessary as part of the refactor, but also simplifies it by
removing a responsibility that doesn't directly belong to the
Environment.

eth/fetcher: fix a log message formatting issue

all: clean up tech debt left behind by the API split

This ensures that package core doesn't depend on package accounts and
resolves an age-old TODO.

Support for legacy version 0.9.x is gone. The compiler version is no
longer cached. Compilation results (and the version) are read directly
from stdout using the --combined-json flag. As a workaround for
ethereum/solidity#651, source code is written to a temporary file before
compilation.

Integration of solc in package ethapi and cmd/abigen is now much simpler
because the compiler wrapper is no longer passed around as a pointer.

Fixes #2806, accidentally

The account manager was previously created by packge cmd/utils as part
of flag processing and then passed down into eth.Ethereum through its
config struct. Since we are starting to create nodes which do not have
eth.Ethereum as a registered service, the code was rearranged to
register the account manager as its own service. Making it a service is
ugly though and it doesn't really fix the root cause: creating nodes
without eth.Ethereum requires duplicating lots of code.

This commit splits utils.MakeSystemNode into three functions, making
creation of other node/service configurations easier. It also moves the
account manager into Node so it can be used by those configurations
without requiring package eth.

rpc: refactor subscriptions and filters

TravisCI: add Go 1.7 targets, bump PPA to 1.7 too

core: ensure the canonical block is written before the canonical hash is set

eth/downloader: fewer headers and futures too in ancestor lookup

Fixes #2872

rpc: client bug fixes

eth/downloader: abort sync if master drops (timeout prev)

eth, eth/downloader: don't forward the DAO challenge header

eth, eth/downloader: better remote head tracking

Makefile, build: move cross compilation into ci.go

core/vm: hide ecrecover error message

Fixes #2825

It's inconsistent not to pass it and most callers will
work with contexts anyway.