[luatex] annoying locale error

[Werner LEMBERG]

>> Unable to read environment locale:exit now.
>
> This is the part of luainit.c where luatex calls setlocale: [...]

Thanks, this helps.  Maybe luatex could emit a more meaningful
message instead?  For example,

```
Unable to read locale data.
Check the 'locale' settings of your environment for consistency.
Exiting now.
```


    Werner