ENH: add intermediate registration stage to act
ENH: add intermediate registration stage to act

the registration within the segmentation step adds substantial
extra time cost.  this commit puts this into a separate stage,
effectively adding a 6th stage.  this also puts the jacobian
calculation at the end of the 4th (optional) stage.

fbudin69500/ANTs,stnava/ANTs,fbudin69500/ANTs,fbudin69500/ANTs,fbudin69500/ANTs,stnava/ANTs,dawnsong/ANTs,dawnsong/ANTs,fbudin69500/ANTs,fbudin69500/ANTs,stnava/ANTs,stnava/ANTs,stnava/ANTs,fbudin69500/ANTs,dawnsong/ANTs,dawnsong/ANTs,dawnsong/ANTs,dawnsong/ANTs,stnava/ANTs,dawnsong/ANTs,stnava/ANTs