Simplified pcl::Registration::getFitnessScore()
Fix hasConverged() for pcl::SampleConsensusInitialAlignment
Fix for distance

In IterativeClosestPoint, the distance given with setMaxCorrespondenceDistance() is taken as
euclidean distance, but in SampleConsensusInitialAlignment as square distance.
Changed SampleConsensusInitialAlignment and registration.getFitnessScore() to take distance
as euclidean distance.