useful real world example of using ST_MaxDistance

git-svn-id: http://svn.osgeo.org/postgis/trunk@11604 b70326c6-7e19-0410-871a-916f4a2858ee
minor adjustment

git-svn-id: http://svn.osgeo.org/postgis/trunk@11605 b70326c6-7e19-0410-871a-916f4a2858ee