COMP: Check for svn executable when using superbuild
COMP: Check for svn executable when using superbuild

LucasGandel/TubeTK,sumedhasingla/TubeTK,aylward/ITKTubeTK,thewtex/TubeTK,sumedhasingla/TubeTK,thewtex/TubeTK,LucasGandel/TubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/TubeTK,aylward/ITKTubeTK,matthieuheitz/TubeTK,sumedhasingla/TubeTK,KitwareMedical/TubeTK,cdeepakroy/TubeTK,LucasGandel/TubeTK,KitwareMedical/TubeTK,cdeepakroy/TubeTK,matthieuheitz/TubeTK,matthieuheitz/TubeTK,cdeepakroy/TubeTK,matthieuheitz/TubeTK,cdeepakroy/TubeTK,aylward/ITKTubeTK,KitwareMedical/ITKTubeTK,thewtex/TubeTK,aylward/ITKTubeTK,LucasGandel/TubeTK,KitwareMedical/TubeTK,sumedhasingla/TubeTK,thewtex/TubeTK