Use a vendor directory for repeatable builds - fixes #816

This is using godep to manage the vendor directory.

vendor/github.com/aws/aws-sdk-go/service/s3/content_md5.go

@@ -0,0 +1,36 @@
+package s3
+
+import (
+	"crypto/md5"
+	"encoding/base64"
+	"io"
+
+	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/aws/request"
+)
+
+// contentMD5 computes and sets the HTTP Content-MD5 header for requests that
+// require it.
+func contentMD5(r *request.Request) {
+	h := md5.New()
+
+	// hash the body.  seek back to the first position after reading to reset
+	// the body for transmission.  copy errors may be assumed to be from the
+	// body.
+	_, err := io.Copy(h, r.Body)
+	if err != nil {
+		r.Error = awserr.New("ContentMD5", "failed to read body", err)
+		return
+	}
+	_, err = r.Body.Seek(0, 0)
+	if err != nil {
+		r.Error = awserr.New("ContentMD5", "failed to seek body", err)
+		return
+	}
+
+	// encode the md5 checksum in base64 and set the request header.
+	sum := h.Sum(nil)
+	sum64 := make([]byte, base64.StdEncoding.EncodedLen(len(sum)))
+	base64.StdEncoding.Encode(sum64, sum)
+	r.HTTPRequest.Header.Set("Content-MD5", string(sum64))
+}