Updated the updateCassiniKernels script to take variable paths (i.e. from...

Updated the updateCassiniKernels script to take variable paths (i.e. from different ISIS versions), created a startup.py script to read the csh startup, created an isis3Startup.py which can set the isis version from Python)

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3647 41f8697f-d340-4b68-9986-7bafba869bb8