pack.FilePackIndex: close mmap object

_load_file_contents may return a mmap object, so self._contents could be
mmap-ed. Close it if so.

Note: we use hasattr() instead of isinstance() for pre-Python 2.6
compatibility (mmap became a class in Python 2.6).
Signed-off-by: Jelmer Vernooij <jelmer@samba.org>

dulwich/pack.py

@@ -360,6 +360,8 @@ class FilePackIndex(PackIndex):
 
     def close(self):
         self._file.close()
+        if getattr(self._contents, "close", None) is not None:
+            self._contents.close()
 
     def __len__(self):
         """Return the number of entries in this pack index."""