extdiff: do single file diffs from the wc with no copy
Extdiff was always making a temporary directory and copying files even when not required. This change makes extdiff avoid the copy when diffing a single file that lives in the wc. This lets external diff tools edit the working copy file directly. It also lets other extensions resuse the functions in extdiff and get in-place diffs.
#header#
<title>#repo|escape#: changelog</title>
<link rel="alternate" type="application/rss+xml"
href="#url#rss-log" title="RSS feed for #repo|escape#">
</head>
<body>
<div class="buttons">
<a href="#url#shortlog/#rev#{sessionvars%urlparameter}">shortlog</a>
<a href="#url#tags{sessionvars%urlparameter}">tags</a>
<a href="#url#file/#node|short#{sessionvars%urlparameter}">manifest</a>
#archives%archiveentry#
<a type="application/rss+xml" href="#url#rss-log">rss</a>
</div>
<h2>changelog for #repo|escape#</h2>
<form action="#url#log">
{sessionvars%hiddenformentry}
<p>
<label for="search1">search:</label>
<input name="rev" id="search1" type="text" size="30">
navigate: <small class="navigate">#changenav%naventry#</small>
</p>
</form>
#entries%changelogentry#
<form action="#url#log">
{sessionvars%hiddenformentry}
<p>
<label for="search2">search:</label>
<input name="rev" id="search2" type="text" size="30">
navigate: <small class="navigate">#changenav%naventry#</small>
</p>
</form>
#footer#