give user option of returning to zxing:// on cancel

git-svn-id: http://zxing.googlecode.com/svn/trunk@2631 59b500cc-1b3d-0410-9834-0bbf25fbcc57
clear redirect after use

git-svn-id: http://zxing.googlecode.com/svn/trunk@2632 59b500cc-1b3d-0410-9834-0bbf25fbcc57