Added x11 lib to isis deps for 64bit systems. Decon has this somehow already....

Added x11 lib to isis deps for 64bit systems.  Decon has this somehow already.  This is needed to check for running X server.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3389 41f8697f-d340-4b68-9986-7bafba869bb8