uhh how could we forget to mention the cool ST_Union(rast,unionarg) is new in PostGIS 2.1.  Got rid of some other notes as its only that annoying ST_Union(rast,uniontype) that's a sore in my back.

git-svn-id: http://svn.osgeo.org/postgis/trunk@11082 b70326c6-7e19-0410-871a-916f4a2858ee