Honor Update::SinglePar properly

Honor Update::SinglePar properly

The SinglePar update flags has been a no-op for a long time without
naybody noticing. This means that the current paragraph was
always rebroken and redrawn, even when only moving the cursor around.

Now we only do that when Update::SinglePar has been specified. This
means that there may be cases where update will not be correct
anymore, because this flag has not been specified. These places will
have to be found and fixed.

Update PAINTING_ANALYSIS.