Unwanted scroll bubbling prevention

i had to reject my previous pull request (and kill branch) so at last this one can be automatically merged

 - 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)

 -  there is pretty <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>)

 - and look at great test case in scrollerSpec