set_props with a complete look read the widget's /MK without resolving
it, so an indirect one started from an empty dictionary: a check box
lost its Cross mark, its 90-degree rotation and any unknown entry, and
the loss survived a save. The /MK is now resolved first, as the
check_style branch already does; a direct /MK behaves as before.
Adds tests::a_whole_look_keeps_the_rest_of_an_indirect_mk, which fails
before this change.
Marco Arnulfo
3e2877cbbb