don't use listdir in make_package script

contrib/make_packages

@@ -25,7 +25,7 @@ if __name__ == '__main__':
 
     os.chdir("dist")
     password = getpass.getpass("Password:")
-    for f in os.listdir("."):
+    for f in [_tgz,_zip]:
         os.system( "gpg --sign --armor --detach --passphrase \"%s\" %s"%(password, f) )
 
     md5_tgz = hashlib.md5(file(_tgz, 'r').read()).digest().encode('hex')