Add list-blobs function to create a lazy-seq of blobs.

list-container is still available as a low-level call, but list-blobs
should be preferred going forward since it doesn't need to be manually
paginated.

blobstore/src/main/clojure/org/jclouds/blobstore.clj

@@ -112,7 +112,8 @@ Options can also be specified for extension modules
       :recursive #(when %2 (.recursive %1))})
 
 (defn list-container
-  "List a container. Options are:
+  "Low-level container listing. Use list-blobs where possible since
+  it's higher-level and returns a lazy seq. Options are:
   :after-marker string
   :in-direcory path
   :max-results n
@@ -131,6 +132,23 @@ Options can also be specified for extension modules
       (.list blobstore container-name list-options))
     (apply list-container *blobstore* blobstore args)))
 
+(defn- list-blobs-chunk [container prefix blobstore & [marker]]
+  (apply blobstore/list-container blobstore container
+         :in-directory prefix (when (string? marker)
+                                [:after-marker marker])))
+
+(defn- list-blobs-chunks [container prefix blobstore marker]
+  (when marker
+    (let [chunk (list-blobs-chunk container prefix blobstore marker)]
+      (lazy-seq (cons chunk
+                      (list-blobs-chunks container prefix blobstore
+                                         (.getNextMarker chunk)))))))
+
+(defn list-blobs
+  "Returns a lazy seq of all blobs in the given container."
+  ([container prefix blobstore]
+     (apply concat (list-blobs-chunks container prefix blobstore :start))))
+
 (defn locations
   "Retrieve the available container locations for the blobstore context."
   ([] (locations *blobstore*))