Fix grid view not updated immediately when marked books changed

Also fix translations for show marked books menu item.

src/calibre/gui2/actions/mark_books.py

@@ -72,7 +72,7 @@ class MarkBooksAction(InterfaceAction):
     def about_to_show_menu(self):
         db = self.gui.current_db
         num = len(db.data.marked_ids)
-        text = ngettext('Show marked book', 'Show marked books (%d)' % num, num)
+        text = _('Show marked book') if num == 1 else (_('Show marked books') + (' (%d)' % num))
         self.show_marked_action.setText(text)
 
     def location_selected(self, loc):

src/calibre/gui2/library/alternate_views.py

@@ -300,6 +300,10 @@ class AlternateViews(object):
             if self.current_book_state[0] is self.current_view:
                 self.current_view.restore_current_book_state(self.current_book_state[1])
             self.current_book_state = None
+
+    def marked_changed(self, old_marked, current_marked):
+        if self.current_view is not self.main_view:
+            self.current_view.marked_changed(old_marked, current_marked)
 # }}}
 
 # Rendering of covers {{{
@@ -818,4 +822,11 @@ class GridView(QListView):
         self.set_current_row(row)
         self.select_rows((row,))
         self.scrollTo(self.model().index(row, 0), self.PositionAtCenter)
+
+    def marked_changed(self, old_marked, current_marked):
+        changed = old_marked | current_marked
+        m = self.model()
+        for book_id in changed:
+            self.update(m.index(m.db.data.id_to_index(book_id), 0))
+
 # }}}

src/calibre/gui2/library/views.py

@@ -690,6 +690,7 @@ class BooksView(QTableView):  # {{{
         self.alternate_views.set_database(db, stage=1)
 
     def marked_changed(self, old_marked, current_marked):
+        self.alternate_views.marked_changed(old_marked, current_marked)
         if bool(old_marked) == bool(current_marked):
             changed = old_marked | current_marked
             sections = tuple(map(self.model().db.data.id_to_index, changed))