Identity of user whose init file is or was read.
The value is nil if `-q' or `--no-init-file' was specified,
meaning do not load any init file.
Otherwise, the value may be an empty string, meaning
use the init file for the user who originally logged in,
or it may be a string containing a user's name meaning
use that person's init file.
In either of the latter cases, `(concat "~" init-file-user "/")'
evaluates to the name of the directory where the init file was
Setting `init-file-user' does not prevent Emacs from loading
`site-start.el'. The only way to do that is to use `--no-site-file'.