Godeps, vendor: convert dependency management to trash (#3198)

This commit converts the dependency management from Godeps to the vendor
folder, also switching the tool from godep to trash. Since the upstream tool
lacks a few features proposed via a few PRs, until those PRs are merged in
(if), use github.com/karalabe/trash.

You can update dependencies via trash --update.

All dependencies have been updated to their latest version.

Parts of the build system are reworked to drop old notions of Godeps and
invocation of the go vet command so that it doesn't run against the vendor
folder, as that will just blow up during vetting.

The conversion drops OpenCL (and hence GPU mining support) from ethash and our
codebase. The short reasoning is that there's noone to maintain and having
opencl libs in our deps messes up builds as go install ./... tries to build
them, failing with unsatisfied link errors for the C OpenCL deps.

golang.org/x/net/context is not vendored in. We expect it to be fetched by the
user (i.e. using go get). To keep ci.go builds reproducible the package is
"vendored" in build/_vendor.

vendor/github.com/syndtr/goleveldb/leveldb/errors/errors.go

@@ -0,0 +1,78 @@
+// Copyright (c) 2014, Suryandaru Triandana <syndtr@gmail.com>
+// All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Package errors provides common error types used throughout leveldb.
+package errors
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/syndtr/goleveldb/leveldb/storage"
+	"github.com/syndtr/goleveldb/leveldb/util"
+)
+
+// Common errors.
+var (
+	ErrNotFound    = New("leveldb: not found")
+	ErrReleased    = util.ErrReleased
+	ErrHasReleaser = util.ErrHasReleaser
+)
+
+// New returns an error that formats as the given text.
+func New(text string) error {
+	return errors.New(text)
+}
+
+// ErrCorrupted is the type that wraps errors that indicate corruption in
+// the database.
+type ErrCorrupted struct {
+	Fd  storage.FileDesc
+	Err error
+}
+
+func (e *ErrCorrupted) Error() string {
+	if !e.Fd.Zero() {
+		return fmt.Sprintf("%v [file=%v]", e.Err, e.Fd)
+	}
+	return e.Err.Error()
+}
+
+// NewErrCorrupted creates new ErrCorrupted error.
+func NewErrCorrupted(fd storage.FileDesc, err error) error {
+	return &ErrCorrupted{fd, err}
+}
+
+// IsCorrupted returns a boolean indicating whether the error is indicating
+// a corruption.
+func IsCorrupted(err error) bool {
+	switch err.(type) {
+	case *ErrCorrupted:
+		return true
+	case *storage.ErrCorrupted:
+		return true
+	}
+	return false
+}
+
+// ErrMissingFiles is the type that indicating a corruption due to missing
+// files. ErrMissingFiles always wrapped with ErrCorrupted.
+type ErrMissingFiles struct {
+	Fds []storage.FileDesc
+}
+
+func (e *ErrMissingFiles) Error() string { return "file missing" }
+
+// SetFd sets 'file info' of the given error with the given file.
+// Currently only ErrCorrupted is supported, otherwise will do nothing.
+func SetFd(err error, fd storage.FileDesc) error {
+	switch x := err.(type) {
+	case *ErrCorrupted:
+		x.Fd = fd
+		return x
+	}
+	return err
+}