title: ScrollView inside Gallery, both scrolling independently
body: <p>I have a Gallery with an adapter which supplies it ScrollViews as its child views.
  I need to make sure that the touch events are handled correctly and as expected:</p>
  
  <ol>
  <li>When the user scrolls horizontally, the gallery scrolls horizontally.</li>
  <li>When the user scrolls vertically, the scroll view scrolls vertically.</li>
  <li>Both scrolls should never happen on the same gesture (the user must lift their finger to scroll the other view).</li>
  <li>Everything must scroll smoothly.</li>
  </ol>
  
  <p>Without overriding any methods, the scroll view is the only thing that scrolls - the gallery never scrolls.</p>
  
  <p>So I understand I need to use onInterceptTouchEvent(...) in the gallery to decide to take over a certain series of MotionEvents but I am unsure how to check if the touch is horizontal or vertical in nature. </p>