Prevent unwanted scroll bubbling

 - it's for <a href="https://github.com/angular-ui/ui-utils/issues/239">issue #239</a> of ui-utils (scrolling over ngScroll intermittently scrolls entire document when bottom of scroll 'page' is reached)

 -  i've added a <a href="http://rawgit.com/dhilt/NGScroller/scroll-prevent/src/examples/scrollBubblingPrevent.html">demo</a> (now accessed from <a href="http://rawgit.com/dhilt/NGScroller/scroll-prevent/src/index.html">index</a>)

 - apart from demo i hardly tried but i can't finish tests for scroll/mousewheel bubbling case; the task of mousewheel simulation for tests is not good-explored task... i will retry it later

 - it may looks strange if FF, but this is normal scroll-within-scroll behaviour in that browser