Fixed #6 dput check local section is failed.

  * This error is using seciont not defined at /etc/dput.cf or ~/.dput.cf.
  * "local" host is defined at /etc/dput.cf in default.
  * Changed using "local" host and raise KeyError when not defined.

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