- added coercen to STIDF for plotKML and kml_layer 
- changed doc of plotKML for STFDF to make "R CMD check --as-cran" happy, it still does not like the Author field in the DESCRIPTION (R 3.1.0)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/plotkml@488 edb9625f-4e0d-4859-8d74-9fd3b1da38cb