Issue #1531: Read fileobj from the current offset, do not seek to
the start.

(will backport to 2.5)
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index ee9922c..ae24291 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1558,7 +1558,8 @@
         self.closed = False
         self.members = []       # list of members as TarInfo objects
         self._loaded = False    # flag if all members have been read
-        self.offset = 0L        # current position in the archive file
+        self.offset = self.fileobj.tell()
+                                # current position in the archive file
         self.inodes = {}        # dictionary caching the inodes of
                                 # archive members already added