Add tarfile from python 2.7

This allow method add in Tarfile to have filter parameter.
This give us filter capa on file to include.
Should be removed when python 2.7 will be the minimum version

installsystems/tarball.py

@@ -11,6 +11,10 @@ import time
 import tarfile
 import StringIO
 import re
+# Use tarfile from python 2.7 which include filter parameter in add method.
+# This is really needed to filter an modify tarball content on the fly.
+# Should be removed when python 2.7 will be the minimum python version
+from installsystems import tarfile
 
 class Tarball(tarfile.TarFile):
     def add_str(self, name, content, ftype, mode):