[fixed] Stack overflow with nested Modals

fixes #893 in the same way tbs fixes it, only allow one listener at a
time

src/Modal.js

@@ -31,9 +31,16 @@ function getContainer(context){
  domUtils.ownerDocument(context).body;
 }
 
+
+
+let currentFocusListener;
+
 /**
  * Firefox doesn't have a focusin event so using capture is easiest way to get bubbling
  * IE8 can't do addEventListener, but does have onfocusin, so we use that in ie8
+ *
+ * We only allow one Listener at a time to avoid stack overflows
+ *
  * @param {ReactElement|HTMLElement} context
  * @param {Function} handler
  */
@@ -42,14 +49,20 @@ function onFocus(context, handler) {
  let useFocusin = !doc.addEventListener;
  let remove;
 
+ if ( currentFocusListener )
+ currentFocusListener.remove();
+
  if (useFocusin) {
  document.attachEvent('onfocusin', handler);
  remove = () => document.detachEvent('onfocusin', handler);
  } else {
  document.addEventListener('focus', handler, true);
  remove = () => document.removeEventListener('focus', handler, true);
  }
- return { remove };
+
+ currentFocusListener = { remove }
+
+ return currentFocusListener;
 }
 
 let scrollbarSize;