fix enviro variable name, speeding up rendering (merge from devbr6)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@56306 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/core/render.py

@@ -404,7 +404,7 @@ class Map(object):
 
         # GRASS environment variable (for rendering)
         self.env = {"GRASS_BACKGROUNDCOLOR" : "FFFFFF",
-               "GRASS_COMPRESSION"     : "0",
+               "GRASS_PNG_COMPRESSION" : "0",
                "GRASS_TRUECOLOR"       : "TRUE",
                "GRASS_TRANSPARENT"     : "TRUE",
                "GRASS_PNG_READ"        : "FALSE",