fixed history deletion. fixed #780

src/main/java/eu/siacs/conversations/services/XmppConnectionService.java

@@ -2086,6 +2086,16 @@ public class XmppConnectionService extends Service implements OnPhoneContactsLoa
 		}
 	}
 
+	public void clearConversationHistory(final Conversation conversation) {
+		conversation.clearMessages();
+		new Thread(new Runnable() {
+			@Override
+			public void run() {
+				databaseBackend.deleteMessagesInConversation(conversation);
+			}
+		}).start();
+	}
+
 	public interface OnConversationUpdate {
 		public void onConversationUpdate();
 	}

src/main/java/eu/siacs/conversations/ui/ConversationActivity.java

@@ -491,7 +491,7 @@ public class ConversationActivity extends XmppActivity implements
 
 					@Override
 					public void onClick(DialogInterface dialog, int which) {
-						conversation.clearMessages();
+						ConversationActivity.this.xmppConnectionService.clearConversationHistory(conversation);
 						if (endConversationCheckBox.isChecked()) {
 							endConversation(conversation);
 						} else {