moved packages from Depends to Imports

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/soiltexture@115 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/soiltexture@116 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/soiltexture@117 edb9625f-4e0d-4859-8d74-9fd3b1da38cb