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/gopkg.in/urfave/cli.v1/errors.go

@@ -0,0 +1,92 @@
+package cli
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+// OsExiter is the function used when the app exits. If not set defaults to os.Exit.
+var OsExiter = os.Exit
+
+// ErrWriter is used to write errors to the user. This can be anything
+// implementing the io.Writer interface and defaults to os.Stderr.
+var ErrWriter io.Writer = os.Stderr
+
+// MultiError is an error that wraps multiple errors.
+type MultiError struct {
+	Errors []error
+}
+
+// NewMultiError creates a new MultiError. Pass in one or more errors.
+func NewMultiError(err ...error) MultiError {
+	return MultiError{Errors: err}
+}
+
+// Error implents the error interface.
+func (m MultiError) Error() string {
+	errs := make([]string, len(m.Errors))
+	for i, err := range m.Errors {
+		errs[i] = err.Error()
+	}
+
+	return strings.Join(errs, "\n")
+}
+
+// ExitCoder is the interface checked by `App` and `Command` for a custom exit
+// code
+type ExitCoder interface {
+	error
+	ExitCode() int
+}
+
+// ExitError fulfills both the builtin `error` interface and `ExitCoder`
+type ExitError struct {
+	exitCode int
+	message  string
+}
+
+// NewExitError makes a new *ExitError
+func NewExitError(message string, exitCode int) *ExitError {
+	return &ExitError{
+		exitCode: exitCode,
+		message:  message,
+	}
+}
+
+// Error returns the string message, fulfilling the interface required by
+// `error`
+func (ee *ExitError) Error() string {
+	return ee.message
+}
+
+// ExitCode returns the exit code, fulfilling the interface required by
+// `ExitCoder`
+func (ee *ExitError) ExitCode() int {
+	return ee.exitCode
+}
+
+// HandleExitCoder checks if the error fulfills the ExitCoder interface, and if
+// so prints the error to stderr (if it is non-empty) and calls OsExiter with the
+// given exit code.  If the given error is a MultiError, then this func is
+// called on all members of the Errors slice.
+func HandleExitCoder(err error) {
+	if err == nil {
+		return
+	}
+
+	if exitErr, ok := err.(ExitCoder); ok {
+		if err.Error() != "" {
+			fmt.Fprintln(ErrWriter, err)
+		}
+		OsExiter(exitErr.ExitCode())
+		return
+	}
+
+	if multiErr, ok := err.(MultiError); ok {
+		for _, merr := range multiErr.Errors {
+			HandleExitCoder(merr)
+		}
+	}
+}