Created attachment 116196 [details] [review]
incomplete attempt to enforce sane UTF-8 string in the D-Bus bindings

(In reply to Patrick Ohly from comment #4)
> I'll have a look at fixing this properly.

My attempt to introduce an explicit "this is an UTF-8 string" type ended up
causing much more changes than hoped for, and still isn't complete (attached).
I stopped when appending a std::pair<std::string, ...> as return value would
not compile because it is treated like appending a parameter - adding a special
exception as for normal return values would break the key point of the exercise
for D-Bus method calls (forcing the caller to think about string content).

So I'll focus instead on silently removing invalid bytes.