unpacker: fix missing arg for py2.4

mercurial/util.py

@@ -236,7 +236,7 b' def unpacker(fmt):'
         return struct.Struct(fmt).unpack
     except AttributeError:
         # 2.4
-        return lambda buf: struct.unpack(fmt)
+        return lambda buf: struct.unpack(fmt, buf)
 
 def popen2(cmd, env=None, newlines=False):
     # Setting bufsize to -1 lets the system decide the buffer size.