Install lua-sec-prosody package on Debian Wheezy and Ubuntu Precise

This is the updated version from the prosody repository because
these distributions have an old version of the lua-sec package
that lacks PFS and other features. Second commit for issue #285.

roles/xmpp/tasks/prosody.yml

 - name: Install Prosody from official repository
   apt: pkg=prosody update_cache=yes
 
+- name: Install lua-sec-prosody on Debian Wheezy and Ubuntu Precise
+  apt: pkg=lua-sec-prosody update_cache=yes
+  when: ansible_distribution_release == 'wheezy' or ansible_distribution_release == 'precise'
+
 - name: Install lua-sec 0.5+
   apt: pkg=lua-sec update_cache=yes
   when: ansible_distribution_release == 'trusty' or ansible_distribution_release == 'jessie'