be quiet on PNG driver open/close (merg from devbr6)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@31266 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.digit/display.c

@@ -197,6 +197,7 @@ void display_bg ( void )
     
     G_debug (2, "display_bg()");
 
+    putenv("GRASS_VERBOSE=0");
     putenv("GRASS_RENDER_IMMEDIATE=TRUE");
     putenv("GRASS_TRUECOLOR=TRUE");