enhanced savanah transition and variant tiles, and minor tweaks to grass.

data/terrain-graphics.cfg

@@ -443,7 +443,9 @@
 {TERRAIN_BASE_PROB            M desert-mountain-peak3     50}
 {TERRAIN_BASE                 M desert-mountains}
 
-{TERRAIN_BASE                 GT savanna}
+{TERRAIN_BASE_PROB            GT savanna	40}
+{TERRAIN_BASE_PROB            GT savanna2	50}
+{TERRAIN_BASE                 GT savanna3}
 {TERRAIN_BASE                 E desert-road}
 {TERRAIN_BASE                 P desert-oasis}