Add support for mouse wheel zooming
Add support for mouse wheel zooming

http://codereview.appspot.com/33051


digideskio/transitfeed,avilaton/transitfeed,zarnold/transitfeed,galvinford/transitfeed,avilaton/transitfeed,bileto/transitfeed,zarnold/transitfeed,bileto/transitfeed,Censio/transitfeed,digideskio/transitfeed,google/transitfeed,bileto/transitfeed,google/transitfeed,Censio/transitfeed,digideskio/transitfeed,zarnold/transitfeed,galvinford/transitfeed,google/transitfeed,Censio/transitfeed,galvinford/transitfeed,avilaton/transitfeed