Sets the cursor theme from which the images for cursor
should be taken.
If the windowing system supports it, existing cursors created
with gdk_cursor_new(), gdk_cursor_new_for_display() and
gdk_cursor_new_from_name() are updated to reflect the theme
change. Custom cursors constructed with
gdk_cursor_new_from_pixbuf() will have to be handled
by the application (GTK+ applications can learn about
cursor theme changes by listening for change notification
for the corresponding #GtkSetting).
a #GdkDisplay
the name of the cursor theme to use, or %NULL to unset
a previously set value
the cursor size to use, or 0 to keep the previous size