In kerneldbgen, added the EXTRA option. Also, added basic support for kerneldb...

In kerneldbgen, added the EXTRA option. Also, added basic support for kerneldb files being specified for SCLK/LSK parameters. Fixes #1023.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5018 41f8697f-d340-4b68-9986-7bafba869bb8