Update to 2.50

Upstream changes:
Changes in version 2.50
-----------------------

* Fix bug https://rt.cpan.org/Ticket/Display.html?id=120231.

* Fix bug https://rt.cpan.org/Ticket/Display.html?id=120300.
  Unfortunately, this withdraws a small part of fix 114999.
  GNU getopt_long() does not accept the (optional)
  argument to be passed to the option without = sign.
  We do, since not doing so breaks existing scripts.

* Provide a default value for options (gnu_compat mode).
  Thanks to Andrew Gregory.

(wen)