Fixes #722.

It makes sense to add a regression test and check that we don't have the same problem in other places. Perhaps we can have a helper function to create stringstreams and clear the locale?

The test failed on mac gcc. It looked like a legitimate failure with the locale stuff but I didn't understand the error. I ran it again anyway, just in case.

Same thing:

terminate called after throwing an instance of 'std::runtime_error'
  what():  locale::facet::_S_create_c_locale name not valid

My guess would be that it needs some packaged installed to get the right locale files. However I'm not sure why it works on clang but not gcc? Maybe they use different standard libraries and the clang library bundles it.

I tried getting to the bottom of this again, but I'm still very confused. One idea that I haven't checked yet is that the locale is just not there, but clang-compiled-version falls back to something "gracefully" and gcc-compiled-version crashes.