We can't use std::locale::global because all streams imbue it by
default and if it's not 'C' (aka std::locale::classic) then we
must imbue all the streams that we don't want localized, and that's
most of them.
Provides error checking for setting the C++ locale from the environment.
This is necessary both because the environment might have an invalid
locale, which would cause an unhandled exception crash.
On windows std::locale("") can't handle some Microsoft-style locale
strings (e.g. Spanish_Spain) so we use boost::locale's gen("") function
to set the locale--though even that can't handle a Microsoft-style
locale string with an appended charset (e.g. Spanish_Spain.1252) and
that's what glibc's setlocale(LC_ALL, NULL) emits.
