bug#29122: eshell passes ARGV[0] as full path to executable

[Eli Zaretskii]

> From: Yegor Timoshenko <yegortimoshenko@gmail.com>
> Date: Fri, 3 Nov 2017 09:22:59 +0000
> 
> The use case here is when programs print usage information.
> 
> Usage: ./a.out command [arguments...]
> Usage: /home/user/path/to/a.out command [arguments...]
> 
> The former reads better and is generally expected from shells.

You will get the same problem when a.out is found by searching PATH.
And on Windows, your program will almost always get argv[0] in
absolute form.  So you need to take care of that anyway, or else your
program will sometimes produce that less readable output.