[Freeciv-Dev] (PR#5450) selection behavior in city report dialog

["John Wheeler" <jdwheeler42@xxxxxxxxx>]

When you select multiple cities and change production, all the
cities stay selected.  But if you select multiple cities and change the
CMA, only one city remains selected.

I suggest a XOR-checked menu or set of radio buttons to determine
selection behavior.  Choices I would want:

* retain all -- when an operation such as change (including proposed
append, first, next) is performed, everything remains selected
* retain fail -- when an operation such as change is performed, only the
ones that failed to change remain selected
* add -- when a selection is made, everything previously selected would
remain (ignored by "No Cities" and "Invert Selection")
* subtract -- selection is made only from previously selected cities
(ignored by "All Cities" and "Invert Selection")

-- 

++JohnWheeler