bug#38181: Actual height of mode-line not taken into account

[martin rudalics]

>> I simply don't yet understand why updating the frame decorations that have 
nothing to do with text layout needs init_iterator to run.  What am I missing?  
Redisplay doesn't in general redraw the whole frame, it only redraws windows.
>
> Answering my own question: because the clear_under_internal_border
> method, which redraws the internal border, is called from
> redisplay_internal.

That's only a secondary issue, I think.  clear_under_internal_border is
called from so many places.  The real reason is, as I tried to explain
before, to update the basic faces, however that is accomplished.

martin