Update to 0.79

Upstream changes:
[Changes for 0.79 - Mon May 18 23:02:11 CST 2015]

* Restore "cpansign --skip" functionality.

  Contributed by: CLOOS

[Changes for 0.78 - Thu Apr  9 16:58:27 CST 2015]

* Fix verify() use from cpanm and CPAN.pm.

  Contributed by: ANDK

[Changes for 0.77 - Wed Apr  8 19:36:50 CST 2015]

* Include the latest public keys of PAUSE, ANDK and AUDREYT.

* Clarify scripts/cpansign copyright to CC0.

  Reported by: @pghmcfc

[Changes for 0.76 - Wed Apr  8 18:05:48 CST 2015]

* Fix signature tests by defaulting to verify(skip=>1)
  when $ENV{TEST_SIGNATURE} is true.

  Reported by: @pghmcfc

[Changes for 0.75 - Tue Apr  7 04:56:09 CST 2015]

Two more issues reported by John Lightsey:

* Update ChangeLog.

* More protection of @INC from relative paths.

Fix various issues reported by John Lightsey:

[Changes for 0.74 - Tue Apr  7 02:39:14 CST 2015]

Fix various issues reported by John Lightsey:

* Fix GPG signature parsing logic.

* MANIFEST.SKIP is no longer consulted unless --skip is given.

* Properly use open() modes to avoid injection attacks.

(wen)