Freeciv

A thing I noticed with the attached experimental savegame was that the plague risk breakdown had two lines with identical descriptions, "Bonus from Aqueduct".

This is because there are two separate effects clauses in effect (one is an additional bonus for Aqueduct before Industrialization), but the effect summary text doesn't mention Industrialization (and nor should it try, probably).

The attached rework merges such duplicate entries, by accumulating the breakdown in a "city_sum" structure. Other benefits of this:

• Gets rid of the duplicate running-total logic that's been a source of bugs (e.g. bug #854306).
• Centralises logic for spotting when the client has incomplete knowledge (added in gna bug #21442).

I've also made it so that the plague risk breakdown shows the bonus value from effects, like e.g. Gold (e.g. "-4.7% : Bonus from Aqueduct+Sewer System (-20%)". (This does show two separate percentages, but I think we are saved from confusion by the second one typically being obviously round numbers matching what you see in the online help.)

One possibly contentious point is the use of two __format(__printf__) qualifiers on a single function with two format strings. My GCC (8.3.0) accepts this and does the right thing with it, but I haven't checked whether it might be a portability hazard.

This touches quite a few strings.