Refactoring cloudfactory layer handler into a more generic storage

middleware concept.

This also breaks the dependency the storage package had on goamz
Signed-off-by: David Lawrence <david.lawrence@docker.com> (github: endophage)

registry.go

@@ -2,6 +2,7 @@ package distribution
 
 import (
 	"io"
+	"net/http"
 	"time"
 
 	"github.com/docker/distribution/digest"
@@ -106,6 +107,11 @@ type Layer interface {
 
 	// CreatedAt returns the time this layer was created.
 	CreatedAt() time.Time
+
+	// ServeHTTP allows a layer to serve itself, whether by providing
+	// a redirect directly to the content, or by serving the content
+	// itself
+	ServeHTTP(w http.ResponseWriter, r *http.Request)
 }
 
 // LayerUpload provides a handle for working with in-progress uploads.