put sampo's FFT into the (new) GTKArdour namespace, to avoid collision with the FFT...

put sampo's FFT into the (new) GTKArdour namespace, to avoid collision with the FFT in the QM DSP library. they should both be namespaced but its easier to avoid changing the QM code at all

git-svn-id: svn://localhost/ardour2/branches/3.0@9056 d708f5d6-7413-0410-9779-e7cbd77b26cf