Log Message:
Update ruby-xmpp4r to 0.5.6.

xmpp4r 0.5.6 (February 14th, 2013)
====================================

* [DOC] Wrong inline documentation in `client.rb`; details of port number
  parameter and removal of un-used 'use_ssl parameter'
* Prevent REXML exceptions on UTF-8 messages
* Fixed broken parse method
* Make sure to open files in binary mode, in order to correctly transfer
  files on Windows
* Prevent REXML exceptions on UTF-8 messages
* Better control of history on muc.join