folks: allow aggregator to be started multiple times

Only the first call has any effect. Matches the D-Bus API
description.

src/dbus/server/pim/folks.cpp

@@ -143,10 +143,13 @@ static void logResult(const GError *gerror, const char *operation)
 
 void IndividualAggregator::start()
 {
-    SYNCEVO_GLIB_CALL_ASYNC(folks_individual_aggregator_prepare,
-                            boost::bind(logResult, _1,
-                                        "folks_individual_aggregator_prepare"),
-                            getFolks());
+    if (!m_started) {
+        m_started = true;
+        SYNCEVO_GLIB_CALL_ASYNC(folks_individual_aggregator_prepare,
+                                boost::bind(logResult, _1,
+                                            "folks_individual_aggregator_prepare"),
+                                getFolks());
+    }
 }
 
 #ifdef ENABLE_UNIT_TESTS

src/dbus/server/pim/folks.h

@@ -250,6 +250,7 @@ class IndividualAggregator
     boost::shared_ptr<FullView> m_view;
     boost::weak_ptr<IndividualAggregator> m_self;
     FolksIndividualAggregatorCXX m_folks;
+    Bool m_started;
 
     IndividualAggregator() {}
 
@@ -273,6 +274,9 @@ class IndividualAggregator
     /**
      * Starts pulling and sorting of contacts.
      * Populates m_view and all other, derived views.
+     * Can be called multiple times.
+     *
+     * See also org.01.pim.contacts.Manager.Start().
      */
     void start();