Fix broken MD5 hash cache.

This change fixes issues causing no matches to occur for existing
objects at S3 in some cases. This issue caused all versions of a
package in a repo to be uploaded again to S3.

Lookups in the cache of file MD5s were failing as the key in the map
had its prefix stripped while the key used for the lookup did not have
the prefix stripped. This change stops stripping the prefix when
building the cache.

Retrieving object MD5s from object metadata (as opposed to the etag
that comes with the object list) were failing as the key in the
metadata map is now "md5" (all lowercase) vs. "Md5" that was used
pre-v2 AWS SDK.

s3/public.go

@@ -191,7 +191,7 @@ func (storage *PublishedStorage) getMD5(path string) (string, error) {
 		return "", err
 	}
 
-	return output.Metadata["Md5"], nil
+	return output.Metadata["md5"], nil
 }
 
 // putFile uploads file-like object to
@@ -431,11 +431,7 @@ func (storage *PublishedStorage) internalFilelist(prefix string, hidePlusWorkaro
 				continue
 			}
 
-			if prefix == "" {
-				paths = append(paths, *key.Key)
-			} else {
-				paths = append(paths, (*key.Key)[len(prefix):])
-			}
+			paths = append(paths, *key.Key)
 			md5s = append(md5s, strings.Replace(*key.ETag, "\"", "", -1))
 		}
 	}