DragonFlyBSD

The return value of setlocale() for LC_ALL deviates from implementations
found in FreeBSD, NetBSD, GNU libc and OpenSolaris. Other implementations
return NULL for unknown locales and the category LC_ALL, where instead
DragonflyBSD isresponding with the internal value list.

Thus an environment variable LC_ALL=fake produces

### setlocale(LC_ALL, "");
C/C/fake/fake/fake/C

### setlocale(LC_CTYPE, "");
(null)

The LC_ALL category is hiding the erroneous effect from the
invoking program, whereas the other categories are correctly
reporting their failures.