Fix various minor mem leaks

src/calibre/gui2/__init__.py

@@ -540,6 +540,7 @@ def choose_dir(window, name, title, default_dir='~'):
             parent=window, name=name, mode=QFileDialog.Directory,
             default_dir=default_dir)
     dir = fd.get_files()
+    fd.setParent(None)
     if dir:
         return dir[0]
 
@@ -560,6 +561,7 @@ def choose_files(window, name, title,
     fd = FileDialog(title=title, name=name, filters=filters,
                     parent=window, add_all_files_filter=all_files, mode=mode,
                     )
+    fd.setParent(None)
     if fd.accepted:
         return fd.get_files()
     return None
@@ -570,6 +572,7 @@ def choose_images(window, name, title, select_only_single_file=True):
                     filters=[('Images', ['png', 'gif', 'jpeg', 'jpg', 'svg'])],
                     parent=window, add_all_files_filter=False, mode=mode,
                     )
+    fd.setParent(None)
     if fd.accepted:
         return fd.get_files()
     return None

src/calibre/gui2/actions/add.py

@@ -243,7 +243,9 @@ def _files_added(self, paths=[], names=[], infos=[], on_card=None):
 
         if hasattr(self._adder, 'cleanup'):
             self._adder.cleanup()
-        self._adder = None
+            self._adder.setParent(None)
+            del self._adder
+            self._adder = None
 
     def _add_from_device_adder(self, paths=[], names=[], infos=[],
                                on_card=None, model=None):

src/calibre/gui2/add.py

@@ -368,6 +368,10 @@ def cleanup(self):
                     shutil.rmtree(self.worker.tdir)
                 except:
                     pass
+        self._parent = None
+        if hasattr(self, 'db_adder'):
+            self.db_adder.setParent(None)
+
 
     @property
     def number_of_books_added(self):