* 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.

ethstats: work around weird URL scheme parsing issues

Fixes #3792 by stripping debug symbols.

core, core/types: use non-pointer receiver for Marshal* methods

accounts/usbwallet: fix Ledger hidapi/libusb protocol violation

Regenerated with fjl/gencodec@1a75a2161009
Also add ,omitempty to optional GenesisAccount fields.

core/types: ensure all EIP155 signer fields are set by deriveSigner

Fixes #3819

build: unify vendor skipping, always run go vet

This ensures 'make test' finds all errors that remote CI would find.
Go 1.7 vet reports a false positive in package log, add a workaround.

core: refactor genesis handling

This commit solves several issues concerning the genesis block:

* Genesis/ChainConfig loading was handled by cmd/geth code. This left
  library users in the cold. They could specify a JSON-encoded
  string and overwrite the config, but didn't get any of the additional
  checks performed by geth.
* Decoding and writing of genesis JSON was conflated in
  WriteGenesisBlock. This made it a lot harder to embed the genesis
  block into the forthcoming config file loader. This commit changes
  things so there is a single Genesis type that represents genesis
  blocks. All uses of Write*Genesis* are changed to use the new type
  instead.
* If the chain config supplied by the user was incompatible with the
  current chain (i.e. the chain had already advanced beyond a scheduled
  fork), it got overwritten. This is not an issue in practice because
  previous forks have always had the highest total difficulty. It might
  matter in the future though. The new code reverts the local chain to
  the point of the fork when upgrading configuration.

The change to genesis block data removes compression library
dependencies from package core.

All uses of ChainConfig.ChainId eventually end up in NewEIP155Signer.
This fixes the case where users forget to set the ChainId in their
config.

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

pow: fix Search with ethash test mode

all: import "context" instead of "golang.org/x/net/context"

There is no need to depend on the old context package now that the
minimum Go version is 1.7. The move to "context" eliminates our weird
vendoring setup. Some vendored code still uses golang.org/x/net/context
and it is now vendored in the normal way.

This change triggered new vet checks around context.WithTimeout which
didn't fire with golang.org/x/net/context.

* les: implement request distributor, fix blocking issues
* core: moved header validation before chain mutex lock

build: require Go >= 1.7

We don't use the opencl build tag anymore.

We have decided to bump the requirement to Go 1.7 because it enables
subtests and allows dropping backwards-compatibility code. This is in
line with Go's support policy. Go 1.6 and earlier no longer receive
security updates.

core/types: use gencodec for JSON marshaling code