Backport change from 1.2.0: src/cavern.c: Add --3d-version option to allow the user to specify the version of the 3d format to output. (ticket#21)
git-svn-id: file:///home/survex-svn/survex/branches/1.0@3682 4b37db11-9a0c-4f06-9ece-9ab7cdaee568