Set locale to ensure dots are recognized as decimal points in SWC files

[adrien-berchet]

In some cases, the function sscanf does not recognize dots as decimal points because of the locale settings of the user (french in my case, so sscanf expects commas as decimal points). This PR ensures that dots are always considered as decimal points in SWC files, regardless of user locale settings.

[mgeplf]

I'll look at this; I've wanted to remove the sscanf for a while; but I'm not super happy about how iostreams handle locales, either. Plus, I think it was slower.

[adrien-berchet]

Ah ok. As you prefer, this is just a quick fix but we could think about something better.

[adrien-berchet]

Is #460 supposed to replace this PR @mgeplf ?

[mgeplf]

Yeah, that's the plan.

[adrien-berchet]

Yeah, that's the plan.

Ok!