Unregister network callbacks from QT gui

Rework the callback system in QT to make this easy, and avoid
leaking window references that prevent the window from being
GC-ed on close

gui/qt/main_window.py

@@ -160,12 +160,10 @@ class ElectrumWindow(QMainWindow, PrintError):
 
         # network callbacks
         if self.network:
-            self.network.register_callback('updated', lambda: self.need_update.set())
-            self.network.register_callback('new_transaction', self.new_transaction)
-            self.register_callback('status', self.update_status)
-            self.register_callback('banner', self.console.showMessage)
-            self.register_callback('verified', self.history_list.update_item)
-
+            self.connect(self, QtCore.SIGNAL('network'), self.on_network_qt)
+            interests = ['updated', 'new_transaction', 'status',
+                         'banner', 'verified']
+            self.network.register_callback(self.on_network, interests)
             # set initial message
             self.console.showMessage(self.network.banner)
 
@@ -194,11 +192,27 @@ class ElectrumWindow(QMainWindow, PrintError):
         self.show()
         self.raise_()
 
-    def register_callback(self, name, method):
-        """ run callback in the qt thread """
-        self.connect(self, QtCore.SIGNAL(name), method)
-        self.network.register_callback(name, lambda *params: self.emit(QtCore.SIGNAL(name), *params))
+    def on_network(self, event, *args):
+        if event == 'updated':
+            self.need_update.set()
+        elif event == 'new_transaction':
+            self.tx_notifications.append(args[0])
+        elif event in ['status', 'banner', 'verified']:
+            # Handle in GUI thread
+            self.emit(QtCore.SIGNAL('network'), event, *args)
+        else:
+            self.print_error("unexpected network message:", event, args)
 
+    def on_network_qt(self, event, *args):
+        # Handle a network message in the GUI thread
+        if event == 'status':
+            self.update_status()
+        elif event == 'banner':
+            self.console.showMessage(args[0])
+        elif event == 'verified':
+            self.history_list.update_item(*args)
+        else:
+            self.print_error("unexpected network_qt signal:", event, args)
 
     def fetch_alias(self):
         self.alias_info = None
@@ -418,10 +432,6 @@ class ElectrumWindow(QMainWindow, PrintError):
          ])
         QMessageBox.information(self, "Electrum - " + _("Reporting Bugs"), msg)
 
-
-    def new_transaction(self, tx):
-        self.tx_notifications.append(tx)
-
     def notify_transactions(self):
         if not self.network or not self.network.is_connected():
             return
@@ -2800,6 +2810,8 @@ class ElectrumWindow(QMainWindow, PrintError):
         NetworkDialog(self.wallet.network, self.config, self).do_exec()
 
     def closeEvent(self, event):
+        if self.network:
+            self.network.unregister_callback(self.on_network)
         self.config.set_key("is_maximized", self.isMaximized())
         if not self.isMaximized():
             g = self.geometry()