Workaround presence subscription loop (fix #115)

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Merge branch 'staging' into production

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>

Conflicts:
	kontalk/xmppserver/component/c2s/resolver.py
Merge branch 'staging'
Merge branch 'production'