Hack to make setLineClass faster when the line already has the given class

Author: marijnh

lib/codemirror.js

@@ -1026,8 +1026,10 @@ var CodeMirror = (function() {
         var no = indexOf(lines, line);
         if (no == -1) return null;
       }
-      line.className = className;
-      changes.push({from: no, to: no + 1});
+      if (line.className != className) {
+        line.className = className;
+        changes.push({from: no, to: no + 1});
+      }
       return line;
     }