add waitWhileSelector()

@@ -904,6 +904,23 @@
             return this.waitFor(function(self) {
                 return self.exists(selector);
             }, then, onTimeout, timeout);
+        },
+
+        /**
+         * Waits until an element matching the provided CSS3 selector does not exist in
+         * remote DOM to process a next step.
+         *
+         * @param  String    selector   A CSS3 selector
+         * @param  Function  then       The next step to perform (optional)
+         * @param  Function  onTimeout  A callback function to call on timeout (optional)
+         * @param  Number    timeout    The max amount of time to wait, in milliseconds (optional)
+         * @return Casper
+         */
+        waitWhileSelector: function(selector, then, onTimeout, timeout) {
+            timeout = timeout ? timeout : this.defaultWaitTimeout;
+            return this.waitFor(function(self) {
+                return ! self.exists(selector);
+            }, then, onTimeout, timeout);
         }
     };