Add a new RadosGW storage engine. Allow engines to distinguish not only between those that can support direct uploads and downloads, but those that support doing it through the browser. Rename resumeable->resumable.

storage/local.py

@@ -1,4 +1,3 @@
-
 import os
 import shutil
 
@@ -80,3 +79,14 @@ class LocalStorage(BaseStorage):
       os.remove(path)
     except OSError:
       pass
+
+  def get_checksum(self, path):
+    path = self._init_path(path)
+    sha_hash = hashlib.sha256()
+    with open(path, 'r') as to_hash:
+      while True:
+        buf = to_hash.read(self.buffer_size)
+        if not buf:
+          break
+        sha_hash.update(buf)
+    return sha_hash.hexdigest()[:7]