Initial attempt to fix predict_rasterEngine when missing values.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/spatial-tools@144 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/spatial-tools@145 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Documentation updates.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/spatial-tools@146 edb9625f-4e0d-4859-8d74-9fd3b1da38cb