Clarified message when nothing to merge is seen.
Sometimes there's a non-tip head waiting to be merged, especially after
pulling in remote changes while there were local modifications in the working
directory which had to be committed before 'hg merge' can work.
#header#
<title>Mercurial Error</title>
</head>
<body>
<h2>Mercurial Error</h2>
<p>
An error occured while processing your request:
</p>
<p>
#error|escape#
</p>
#footer#