XMPPRoster: Add getter for the connection.

src/XMPPRoster.h

@@ -78,6 +78,11 @@
 }
 
 #ifdef OF_HAVE_PROPERTIES
+/**
+ * \brief The connection to which the roster belongs
+ */
+@property (readonly, assign) XMPPConnection *connection;
+
 /**
  * \brief An object for data storage, conforming to the XMPPStorage protocol.
  *
@@ -143,6 +148,8 @@
  */
 - (void)removeDelegate: (id <XMPPRosterDelegate>)delegate;
 
+- (XMPPConnection*)connection;
+
 - (void)setDataStorage: (id <XMPPStorage>)dataStorage;
 - (id <XMPPStorage>)dataStorage;