fececve man page

[Simone Piccardi <piccardi@xxxxxxxxxxx>]

In http://man7.org/linux/man-pages/man3/fexecve.3.html in the reported 
errors there are only EINVAL and ENOSYS but in the BUGS section is cited 
also ENOENT (I suppose coming from execveat) for trying to use a script.

Furthermore I think that ENOSYS should be cited as present only when 
fexecve is not implemented using execveat.

Regards
Simone