[PATCH] Improve execl* functions

[R. Diez]

Hallo Federico Terraneo:

> The complexity is caused by POSIX.1-2008 which
> [...]
> allows individual targets to define _EXECL_USE_MALLOC

The reason why _EXECL_USE_MALLOC exists in your patch is well explained in your e-mail, but an e-mail is not the right place for documentation.

In order to help future developers looking at the code, I would place the reason as a comment over the first "#ifndef _EXECL_USE_MALLOC".

Best regards,
   rdiez