git-svn-id: https://arducopter.googlecode.com/svn/trunk@3248 f9c3cf11-9bcb-44bc-f272-b75c42450872
this gives us the number of bytes available in the transmit buffer for a mavlink channel git-svn-id: https://arducopter.googlecode.com/svn/trunk@3246 f9c3cf11-9bcb-44bc-f272-b75c42450872
git-svn-id: https://arducopter.googlecode.com/svn/trunk@924 f9c3cf11-9bcb-44bc-f272-b75c42450872