TileConstants: impl isIndestructible2(), slightly different than isIndestructible()

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

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@799 d9718cc8-9f43-0410-858b-315f434eb58c
buildings: define large zone structures in tiles.rc
buildings: implement zonePlopNew() to place a zone using info in tiles.rc

Take note that the argument given to this function is not the upper-left
tile value, but rather the "zone" tile for the building.
buildings: replace callers of zonePlop() with calls to zonePlopNew()
buildings: remove obsolete zonePlop()
buildings: rename zonePlopNew() to zonePlop()