Increases the number of clients that show the please wait window. The implementing class is responsible for holding a counter internally which a call to this method will increase.
As long as the internal counter is not zero (0), the please wait window will stay visible. To decrease the counter, make a call to Pop. A call to Show(string) or one of its overloads will not increase the internal counter. A call to Hide will reset the internal counter to zero (0) and thus hide the window.