config: add sanity assert that files are opened as binary
This helps with some debugging in Python 3, and shouldn't hurt
anything in Python 2. The unusual construction using getattr is done
so that StringIO/BytesIO instances can be used as well as real files.
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<link rel="icon" href="{staticurl|urlescape}hgicon.png" type="image/png">
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="{staticurl|urlescape}style.css" type="text/css" />
<script type="text/javascript" src="{staticurl|urlescape}mercurial.js"></script>