Ambiguous occurrence ‘stdout’, and likewise ‘stderr’, when trying to doctest turtle script

usually I run doctests on my Haskell programs, like so:

```
$ doctest -DDOCTEST somefile.hs
```
when I do this with a minimal turtle script, like this one:
```haskell
#!/usr/bin/env runturtle

{-# LANGUAGE CPP #-}

#ifdef DOCTEST
-- stuff here usually
#endif

import Turtle

main = return ()
```
(having defined a separate runturtle script for that matter)

```shell
#!/bin/sh
exec cabal exec runhaskell -- "$@"
```

I get error messages:
```
rx@mirabelle {master} ~/cfg/spin $ doctest -DDOCTEST somefile.hs

:5:14: error:
Ambiguous occurrence ‘stdout’
It could refer to either ‘Turtle.stdout’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stdout’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)

:5:21: error:
Ambiguous occurrence ‘stderr’
It could refer to either ‘Turtle.stderr’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stderr’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)

:7:15: error:
Ambiguous occurrence ‘stdout’
It could refer to either ‘Turtle.stdout’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stdout’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)

:9:15: error:
Ambiguous occurrence ‘stderr’
It could refer to either ‘Turtle.stderr’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stderr’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)

:11:14: error:
Ambiguous occurrence ‘stdout’
It could refer to either ‘Turtle.stdout’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stdout’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)

:13:14: error:
Ambiguous occurrence ‘stderr’
It could refer to either ‘Turtle.stderr’,
imported from ‘Turtle’ at somefile.hs:12:1-13
(and originally defined in ‘Turtle.Prelude’)
or ‘System.IO.stderr’,
imported from ‘System.IO’
(and originally defined in ‘GHC.IO.Handle.FD’)
Examples: 0 Tried: 0 Errors: 0 Failures: 0
rx@mirabelle {master} ~/cfg/spin $
```
not sure how to best cope with that situation, using
```
{-# LANGUAGE NoImplicitPrelude #-}
```
causes me a lot of pain to import everything I need by hand

maybe I am doing something wrong? my turtle script runs just fine though,
it's just the fact that I cannot doctest it, that's annoying me

I can calm down the error msgs with
```
import Turtle hiding (stderr, stdout)
```
but really I would prefer Turtle's stderr/stdout over the ones from System.IO/Prelude
and thus stay in my Turtle world. however

```
import Prelude hiding (stderr, stdout)
import Turtle
```
does not help (I still get the errors above ?)

thanks

-Andreas

Start with the minimal Turtle script and the `doctest -DDOCTEST somefile.hs` command shown in the report; inspect Turtle's exported `stdout` and `stderr` names and how doctest loads imports. Done means the reproducer can be doctested without ambiguous-occurrence errors while preserving the intended Turtle handles.

Written by the indexing model from the issue text.