Resolved the backward compatibility for python_gnupg 0.3.0 (Wheezy version).
Resolved the backward compatibility for python_gnupg 0.3.0 (Wheezy version).

  :class:`GPG` object has status attribute in python_gnupg version 0.3.6,
  but 0.3.0 version does not have this attribute.
  python-gnupg version of Debian GNU/Linux Wheezy is 0.3.0.
  So changed use "timestamp" attribute that 0.3.0 has also.

Signed-off-by: Kouhei Maeda <c9f1823971fa1a4c79cdb50b3311094021cee31e@palmtb.net>

mkouhei/pydebsign,mkouhei/pydebsign