Fix for compilation errors in Registration module.

typename is missing in the clone function of CorrespondenceEstimation classes. 

    typename CorrespondenceEstimation<PointSource, PointTarget, Scalar>::Ptr copy (new CorrespondenceEstimation<PointSource, PointTarget, Scalar> (*this));

Alternatively it is also possible to use Ptr directly:

    Ptr copy (new CorrespondenceEstimation<PointSource, PointTarget, Scalar> (*this));

MacOSX 10.6.8, gcc-4.2.1