ServiceDiscoveryManager: Anounce 'disco#info' and 'disco#items' on service discovery queries in accordance with XEP-0030

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13464 b35dd754-fafc-0310-a699-88a17e54d16e
ServiceDiscoveryManager: Use 'Set' as data structure for features to prevent reporting duplicate features

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13465 b35dd754-fafc-0310-a699-88a17e54d16e