hgweb: rely on a specific class to change cursor type in followlines UI

hgweb: rely on a specific class to change cursor type in followlines UI

The previous CSS rule would also apply in pages where followlines UI was not
available (e.g. "changeset" view at /rev/<node>/). We insert a
"followlines-select" class in JavaScript on actually selectable lines and
restrict the CSS selector to use it.

--- a/mercurial/templates/static/linerangelog.js	Mon Apr 03 09:40:25 2017 +0200
+++ b/mercurial/templates/static/linerangelog.js	Mon Apr 03 09:58:36 2017 +0200
@@ -22,6 +22,11 @@
         sourcelines.children,
         function(x) { return x.tagName === 'SPAN' });
 
+    // add a "followlines-select" class to change cursor type in CSS
+    for (var i = 0; i < spans.length; i++) {
+        spans[i].classList.add('followlines-select');
+    }
+
     var lineSelectedCSSClass = 'followlines-selected';
 
     //** add CSS class on <span> element in `from`-`to` line range */

--- a/mercurial/templates/static/style-paper.css	Mon Apr 03 09:40:25 2017 +0200
+++ b/mercurial/templates/static/style-paper.css	Mon Apr 03 09:58:36 2017 +0200
@@ -280,7 +280,7 @@
   background-color: #bfdfff;
 }
 
-div.overflow pre.sourcelines > span:hover {
+div.overflow pre.sourcelines > span.followlines-select:hover {
   cursor: cell;
 }