Some implementations of C++ streams (notably libstdc++ under OS X) are buggy
and change the global locale to implement support for imbue(), which is not
thread-safe, and so could introduce subtle bugs in multi-thread programs.

Replace the old correct but not working in practice code with a new ugly
version only supporting decimal comma and period which is not totally correct
in theory but should work fine in practice (and shouldn't make things worse
even for the hypothetical locales using some other decimal separator anyhow).