Don't fail on submodules

Submodules will get listed prefixed with a '@', using a specific CSS class for
styling. The href will be set to the url of the submodule.
Filesize will appear as 0 and filemode will not be printed to avoid an awkward
mode: "?---------".

In writefilestree, we don't return anymore if an entry can't be categorized as
an object, but rather, fail if we can't retrieve its name.

style.css

@@ -58,6 +58,10 @@ table td {
 	white-space: normal;
 }
 
+a.module {
+	color: #777;
+}
+
 td.num {
 	text-align: right;
 }