[bug] problem with env vars that zsh sets itself

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

zsh's "export" command doesn't list the environment variables
that zsh sets itself.

$ env -i zsh -xc 'export;env'
+zsh:1> export
+zsh:1> env
HOME=/home/stephane
LOGNAME=stephane
SHLVL=0
PWD=/home/stephane
OLDPWD=/home/stephane
_=/usr/bin/env

Actually, it's as if they were not given the "export" flag even
though they are passed to the environment of executed commands:

$ env -i zsh -c 'typeset -p HOME SHLVL'
typeset HOME=/home/stephane
typeset -i10 SHLVL=1

$ zsh --version
zsh 5.2 (x86_64-debian-linux-gnu)

Seems to be a regression. It used to work OK in 4.1.1

-- 
Stephane