avoid adding ./ to urls unnecessarily

This avoids constructing urls like "./../foo/".
The leading "../" avoids any colon confusion already.

I noticed in my logs that certain badly written web spiders (hello again,
Yahoo!) fail to follow urls like ikiwiki was constructing to the right
place (instead ending up at "./foo/")

IkiWiki.pm

@@ -942,9 +942,9 @@ sub beautify_urlpath ($) { #{{{
 		$url =~ s!/index.$config{htmlext}$!/!;
 	}
 
-	# Ensure url is not an empty link, and
-	# if it's relative, make that explicit to avoid colon confusion.
-	if ($url !~ /^\//) {
+	# Ensure url is not an empty link, and if necessary,
+	# add ./ to avoid colon confusion.
+	if ($url !~ /^\// && $url !~ /^\.\.\//) {
 		$url="./$url";
 	}