add an id to the categories <ul> elements (#4784)

extra/modules/root.py

@@ -1001,7 +1001,7 @@ class AlternateRootDirectory(OldRootDirectory):
             if not formdefs and not formdefs_advertise:
                 continue
 
-            r += htmltext('<li>')
+            r += htmltext('<li id="category-%s">') % category.url_name
             r += htmltext('<strong>')
             r += htmltext('<a href="%s/">') % category.url_name
             r += category.name