ENH:  Adding generic computation type.

Currently the point set metrics are only compatible with
computation type of double.  This patch extends the
metrics to a possible float type.

Change-Id: I589a5882591a73302104b089554e33bb4ee589dd
Merge branch 'master' of git://itk.org/ITK

Change-Id: Ic30e8b581aa851ea7db2cab91bdb1016ca4a8d08
Merge topic 'PointSetMetricComputationType'

a1b2b9fb Merge branch 'master' of git://itk.org/ITK
5c081872 ENH:  Adding generic computation type.