Fix authenticated HTTP uploads in recent Python3

Closes: https://bugs.debian.org/944194

get_full_url() was changed to full_url by https://github.com/python/cpython/commit/6c5e28c383bf587f80d01e52f887801be200200d (3.1).

headers.get() was changed to get_header() by https://github.com/python/cpython/commit/783737625d1f06f78b53eee6331d2f428ffe4d27 (3.4)