More cleanup,

More cleanup,

* hildon-widgets/hildon-dialoghelp.h: use G_BEGIN_DECLS +
        coding style cleanup

        * hildon-widgets/hildon-color-popup.h: likewise.

        * hildon-widgets/hildon-color-popup.[ch] (hildon_color_popup_new):
        use const parameter

        * hildon-widgets/hildon-color-selector.c
        (hildon_color_selector_new): use g_return_val_if_fail instead of
        g_assert.
        (select_color): use g_assert instead of g_return_if_fail

        * hildon-widgets/hildon-calendar-popup.c
        (hildon_calendar_allow_exit): use g_assert instead of g_return_if_fail.