Backport from trunk

--HG--
branch : setuptools-0.6
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/branches/setuptools-0.6%4085332

setuptools/archive_util.py

@@ -185,10 +185,10 @@ def unpack_tarfile(filename, extract_dir, progress_filter=default_filter):
             if not name.startswith('/') and '..' not in name:
                 dst = os.path.join(extract_dir, *name.split('/'))
 
-                while member.islnk() or member.issym():
+                while member is not None and member.islnk() or member.issym():
                     member = tarobj._getmember(member.linkname, member)
     
-                if member.isfile() or member.isdir():
+                if member is not None and member.isfile() or member.isdir():
                     dst = progress_filter(name, dst)
                     if dst:
                         if dst.endswith(os.sep):