use zsh and fish as login shell

[宋文武]

My previous patches for bash/zsh did not put fish into consider.
It's not POSIX-compliant, I have to generate a different config file.

Gentoo/Exherho create different files for differnt shells, eg:
  /etc/profile.env for sh
  /etc/profile.csh for csh
both comming from /etc/env.d.

So, I could do something similar:

env.scm
Description: Text document

WDYT?

Since I'm new to Guile, please don't be hesitate to correct me (style,
name, etc..).
Thanks!