Replace godep with vndr

Vndr has a simpler configuration and allows pointing to forked
packages. Additionally other docker projects are now using
vndr making vendoring in distribution more consistent.

Updates letsencrypt to use fork.
No longer uses sub-vendored packages.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

vendor/github.com/miekg/dns/singleinflight.go

@@ -0,0 +1,57 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Adapted for dns package usage by Miek Gieben.
+
+package dns
+
+import "sync"
+import "time"
+
+// call is an in-flight or completed singleflight.Do call
+type call struct {
+	wg   sync.WaitGroup
+	val  *Msg
+	rtt  time.Duration
+	err  error
+	dups int
+}
+
+// singleflight represents a class of work and forms a namespace in
+// which units of work can be executed with duplicate suppression.
+type singleflight struct {
+	sync.Mutex                  // protects m
+	m          map[string]*call // lazily initialized
+}
+
+// Do executes and returns the results of the given function, making
+// sure that only one execution is in-flight for a given key at a
+// time. If a duplicate comes in, the duplicate caller waits for the
+// original to complete and receives the same results.
+// The return value shared indicates whether v was given to multiple callers.
+func (g *singleflight) Do(key string, fn func() (*Msg, time.Duration, error)) (v *Msg, rtt time.Duration, err error, shared bool) {
+	g.Lock()
+	if g.m == nil {
+		g.m = make(map[string]*call)
+	}
+	if c, ok := g.m[key]; ok {
+		c.dups++
+		g.Unlock()
+		c.wg.Wait()
+		return c.val, c.rtt, c.err, true
+	}
+	c := new(call)
+	c.wg.Add(1)
+	g.m[key] = c
+	g.Unlock()
+
+	c.val, c.rtt, c.err = fn()
+	c.wg.Done()
+
+	g.Lock()
+	delete(g.m, key)
+	g.Unlock()
+
+	return c.val, c.rtt, c.err, c.dups > 0
+}