vcs_info causing LC_MESSAGES to be unset

[Jeremy Cantrell <jmcantrell@xxxxxxxxx>]

In my zshrc I have the following (among other things):

```zsh
setopt prompt_subst
autoload -U vcs_info
precmd_functions+=vcs_info
```

Before this is executed, `locale` reports my `LC_MESSAGES` to be the
same value as my `LANG`, "en_us.UTF-8". After the first time the
function is called, `LC_MESSAGES` is set to an empty string. I notice
in the function, `LC_MESSAGES` is declared as local for autoexport and
then set to "C".

Why would this be causing it to be an empty string in my environment?
It seems wrong that it should be changing those values for anything
outside of whatever is using it within `vcs_info`.