bundle: make unbundle object seekable

bundle: make unbundle object seekable

This is only for uncompressed bundles used by bundlerepo.

--- a/mercurial/changegroup.py	Fri Sep 17 19:02:26 2010 -0500
+++ b/mercurial/changegroup.py	Fri Sep 17 19:02:32 2010 -0500
@@ -146,6 +146,10 @@
         return self._type != 'UN'
     def read(self, l):
         return self._stream.read(l)
+    def seek(self, pos):
+        return self._stream.seek(pos)
+    def tell(self):
+        return self._stream.tell(pos)
 
 class headerlessfixup(object):
     def __init__(self, fh, h):