replace GDK_IS_WINDOW with GDK_IS_DRAWABLE in the assert, only check

replace GDK_IS_WINDOW with GDK_IS_DRAWABLE in the assert, only check

Sat Apr 20 16:49:26 2002  Kristian Rietveld  <kris@gtk.org>

        * gdk/x11/gdkpixmap-x11.c (gdk_pixmap_new): replace GDK_IS_WINDOW
        with GDK_IS_DRAWABLE in the assert, only check GDK_WINDOW_DESTROYED
        if window is a GdkWindow,
        (gdk_bitmap_create_from_data): ditto,
        (gdk_pixmap_create_from_data): ditto