os: Fix 64-bit Linux support.

ino_t and off_t types (d_ino and d_off fields) appear to be defined as unsigned
long on Linux.

TODO: Move readdir wrapper function to C, because DIRENT layout is inherently
OS-specific.

os/os/__init__.py

@@ -105,7 +105,7 @@ def ilistdir_ex(path="."):
     if not dir:
         raise_error()
     res = []
-    dirent_fmt = "iiHB256s"
+    dirent_fmt = "LLHB256s"
     while True:
         dirent = readdir_(dir)
         if not dirent: