hgweb: color line which is linked to in file source view

hgweb: color line which is linked to in file source view

Browser compatibility (':target' selector used): IE 8+, FF 3.5+, Safari 3.1+,
Opera 9.5+, Chromium 4+, all popular mobile browsers.

--- a/mercurial/templates/static/style-paper.css	Thu Jul 04 14:19:13 2013 +0400
+++ b/mercurial/templates/static/style-paper.css	Thu Jul 04 14:19:43 2013 +0400
@@ -240,6 +240,10 @@
 .sourcelines > span:nth-child(4n+1) { background-color: #f0f0f0; }
 .sourcelines > span:nth-child(4n+3) { background-color: white; }
 
+.sourcelines > span:target {
+  background-color: #ffff99;
+}
+
 .sourcelines > a {
     display: inline-block;
     position: absolute;