New ice transitions by pekka.

Uses 2 layers of transition tiles for ice to water with an aditional
submerged part which is layered lower in the stack to not overlap
adjacent trans of other terrain.

data/terrain-graphics.cfg

@@ -770,6 +770,7 @@
 
 {SET_ADJACENT_FLAG         Qq      K                kscZ\|/Y           transition2}
 {TERRAIN_ADJACENT_CUSTOM   -500    CKnNo            kscZ\|/Y           castle-to-water transition2}
+{TERRAIN_ADJACENT_CUSTOM   -510    i                kscZ\|/wY	       ice-to-water submerged_part}
 
 {TERRAIN_ADJACENT          -520    cZ\|/            !cZ\|/m             coast}
 {TERRAIN_ADJACENT          -530    k                !k                  ford}