named locale error checking

[Benjamin Kosnik]

> Should be OK.  No standard assumes details about the locale
> implementation and therefore they don't mention something like
> incomplete information.  This is normally left for the implementation
> to define.

Cool, that's what I figured. I'll go ahead and do this. 

Is there a list of "complete" glibc locales?

I've looked through xlocale.h/langinfo.h/locale.h and can't seem to find 
error codes for the numeric bits. Say:

  // Named locale.
	  _M_decimal_point = *(__nl_langinfo_l(RADIXCHAR, __cloc));
	  _M_thousands_sep = *(__nl_langinfo_l(THOUSEP, __cloc));
	  _M_grouping = __nl_langinfo_l(GROUPING, __cloc);

How can I find out what is an "failed" call to __nl_langinfo_l for the 
various nl_items?

-benjamin