compatibility with doc.cls and verbatim

I'm not sure why, but the following does not compile:
```tex
\documentclass{article}
\usepackage{doc}
\usepackage{microtype}
\begin{document}
\begin{verbatim}

a
\end{verbatim}
\end{document}
```

the error is
```tex
! Argument of \check@percent has an extra }.
<inserted text> 
                \par
```

and it goes into a loop, so something in the par hook or `\everypar` maybe.