added a define to make compilation optional git-svn-id: https://arducopter.googlecode.com/svn/trunk@3031 f9c3cf11-9bcb-44bc-f272-b75c42450872
git-svn-id: https://arducopter.googlecode.com/svn/trunk@3019 f9c3cf11-9bcb-44bc-f272-b75c42450872