doc fix: hg tags defaults to current parent revision, too.
Additionally use better language for the help text for tag,
cat and manifest.
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" />