bugfix: Wrong state for scrollbound scenes

When the duration is >0 the scene state should be DURING, when the
scroll position equals the scene's start position.

fixes janpaepke#299

dev/src/ScrollMagic/Scene/core.js

@@ -258,12 +258,12 @@ this.progress = function (progress) {
  _state = _progress === 0 ? 'BEFORE' : 'DURING';
  } else {
  // scenes with start and end
- if (progress <= 0 && _state !== 'BEFORE' && reverseOrForward) {
+ if (progress < 0 && _state !== 'BEFORE' && reverseOrForward) {
  // go back to initial state
  _progress = 0;
  _state = 'BEFORE';
  doUpdate = true;
- } else if (progress > 0 && progress < 1 && reverseOrForward) {
+ } else if (progress >= 0 && progress < 1 && reverseOrForward) {
  _progress = progress;
  _state = 'DURING';
  doUpdate = true;
@@ -302,4 +302,4 @@ this.progress = function (progress) {
 
  return Scene;
  }
-};
+};