convert: make contents of "extra" dict available from sources, for sinks.
This breaks hash preservation for hg->hg conversion, as each converted
change gets a convert_revision item added to its extra dict. Ugh.
Content-type: text/html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="icon" href="?static=hgicon.png" type="image/png">
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="?static=style.css" type="text/css" />