Update security/openpam to openpam-20071221 (Hydrangea).  Changes from
version 20050616 (Figwort) include:

- ENHANCE: API function arguments are now const where appropriate, to
  match corresponding changes in the Solaris PAM and Linux-PAM APIs.

- ENHANCE: corrected a number of C namespace violations.

- ENHANCE: the module cache has been removed, allowing long-lived
  applications to pick up module changes.  This also allows multiple
  threads to use PAM simultaneously (as long as they use separate PAM
  contexts), since the module cache was the only part of OpenPAM that
  was not thread-safe.

(jlam)