Consistently set c and c++ locale.

[tomasbrod]

Apparently only c stdio locale is set.
Also set std::locale::classic for serialization ostringstreams.

[denravonska]

Additionally we only need to set std::locale once on startup and not every time we convert a double as we do now.

[tomasbrod]

You mean this? For me it does not look like causing problems.

[denravonska]

Yeah. I get a warning on it, I assume to the std::locale::classic() call when done from different threads. No idea what's going on under the hood there.

[jamescowens]

I don't think this is an issue anymore?