py3: fix manifestdict.fastdelta() to be compatible with memoryview This doesn't look nice, but a straightforward way to support Python 3. bytes(m[start:end]) is needed because a memoryview doesn't support ordering operations. On Python 2, m[start:end] returns a bytes object even if m is a buffer, so calling bytes() should involve no additional copy. I'm tired of trying cleaner alternatives, including: a. extend memoryview to be compatible with buffer type => memoryview is not an acceptable base type b. wrap memoryview by buffer-like class => zlib complains it isn't bytes-like