TileConstants: make isIndestructible()

continuing the trend of moving tile number logic to centralized location

git-svn-id: http://micropolis.googlecode.com/svn/trunk@798 d9718cc8-9f43-0410-858b-315f434eb58c
TileConstants: impl isIndestructible2(), slightly different than isIndestructible()

the difference is whether RUBBLE is included or not;
TODO- make a better name

git-svn-id: http://micropolis.googlecode.com/svn/trunk@799 d9718cc8-9f43-0410-858b-315f434eb58c