use alt+click drag for moving reply box

contrib/js/backlink.js

@@ -332,7 +332,9 @@ function init(prefix) {
   e.addEventListener("dragstart", function(ev) {
     mouseDownX = ev.clientX;
     mouseDownY = ev.clientY;
-    ev.preventDefault();
+    if (!ev.altKey) {
+      ev.preventDefault();
+    }
   }, false);
   
   e.addEventListener("dragend", function(ev) {
@@ -343,7 +345,9 @@ function init(prefix) {
     rpl.moveTo(x, y);
     originalX = x;
     originalY = y;
-    ev.preventDefault();
+    if (!ev.altKey) {
+      ev.preventDefault();
+    }
   }, false);
 
   // add replyto post handlers