make "get roster" command work with recent clients

xep 0093: http://xmpp.org/extensions/xep-0093.html
xep 0144: http://xmpp.org/extensions/xep-0144.html

basicaly, they differ with namespace and new action attribute for <item>
element. (also, xep 0093 does not work with psi, xep 0144 does.)
Merge pull request #29 from hiciu/xep-0144

make "get roster" command work with recent clients