[PATCH] improve checks on usernames V3.

[Ralf Friedl]

Tito wrote:
> Hi,
> minor improvements vs. v2 patch:
> 1) some more comments added.
> 2) we now print the position of the illegal character.
>
> ...
> 		/* We don't use isalnum  as it will allow locale-specific non-ASCII */
> 		/* letters in legacy 8-bit locales. *
What is the problem with locale-specific characters?
I have used user and group names with UTF-8 characters and I didn't 
notice a problem so far.
GNU ls even adjusts the width of the user and group names properly for 
UTF-8 names, which would be useless if such names can't be created. 
(Side note, Busybox ls does not adjust the width and truncates at 8 bytes).

Ralf