Fixed parent function return ownership.

Fixed QMainWindow functions ownership.

Fixes #241.

Reviewer: Hugo Parente Lima <hugo.lima@openbossa.org>,
          Marcelo Lira <marcelo.lira@openbossa.org>

tests/QtGui/qmainwindow_test.py

@@ -17,6 +17,14 @@ class MainWindow(QtGui.QMainWindow):
         pointerToolbar = self.addToolBar("Pointer type")
         pointerToolbar.addWidget(pointerButton)
 
+class MyButton(QtGui.QPushButton):
+    def __init__(self, parent=None):
+        QtGui.QPushButton.__init__(self)
+        self._called = False
+
+    def myCallback(self):
+        self._called = True
+
 
 class TestMainWindow(UsesQApplication):
 
@@ -26,6 +34,40 @@ class TestMainWindow(UsesQApplication):
         QtCore.QTimer.singleShot(1000, self.app.quit)
         self.app.exec_()
 
+    def testRefCountToNull(self):
+        w = QtGui.QMainWindow()
+        c = QtGui.QWidget()
+        self.assertEqual(sys.getrefcount(c), 2)
+        w.setCentralWidget(c)
+        self.assertEqual(sys.getrefcount(c), 3)
+        w.setCentralWidget(None)
+        self.assertEqual(sys.getrefcount(c), 2)
+
+    def testRefCountToAnother(self):
+        w = QtGui.QMainWindow()
+        c = QtGui.QWidget()
+        self.assertEqual(sys.getrefcount(c), 2)
+        w.setCentralWidget(c)
+        self.assertEqual(sys.getrefcount(c), 3)
+
+        c2 = QtGui.QWidget()
+        w.setCentralWidget(c2)
+        self.assertEqual(sys.getrefcount(c), 2)
+        self.assertEqual(sys.getrefcount(c2), 3)
+
+    def testSignalDisconect(self):
+        w = QtGui.QMainWindow()
+        b = MyButton("button")
+        b.clicked.connect(b.myCallback)
+        w.setCentralWidget(b)
+
+        b = MyButton("button")
+        b.clicked.connect(b.myCallback)
+        w.setCentralWidget(b)
+
+        b.click()
+        self.assertEqual(b._called, True)
+
 
 if __name__ == '__main__':
     unittest.main()