Changed the version number from 3 to 4 in mdiscal by request of the MESSENGER...

Changed the version number from 3 to 4 in mdiscal by request of the MESSENGER team.  References #1186

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4802 41f8697f-d340-4b68-9986-7bafba869bb8