Fixed DiskLruCache file naming

Author: nostra13

library/src/main/java/com/nostra13/universalimageloader/cache/disc/impl/ext/DiskLruCache.java

@@ -964,11 +964,11 @@ private IOException invalidLengths(String[] strings) throws IOException {
 		}
 
 		public File getCleanFile(int i) {
-			return new File(directory, key + "" + i);
+			return new File(directory, key + "." + i);
 		}
 
 		public File getDirtyFile(int i) {
-			return new File(directory, key + "" + i + ".tmp");
+			return new File(directory, key + "." + i + ".tmp");
 		}
 	}
 }