git-svn-id: svn://svn.r-forge.r-project.org/svnroot/spatial-tools@147 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added additional_header flags to create_blank_raster and build_raster_header.  focal_hpc and rasterEngine should now build the additional_headers BEFORE starting the run.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/spatial-tools@148 edb9625f-4e0d-4859-8d74-9fd3b1da38cb