tile animation: cleanup, remove obsolete ANIMBIT constant

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@737 d9718cc8-9f43-0410-858b-315f434eb58c
tile animation: another cleanup item - unpowered zone should not animate

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@738 d9718cc8-9f43-0410-858b-315f434eb58c
tile animation: synthesize ANIMBIT when saving (for compatibility)

Also, add some safety checks in case Tiles.get() is called with an out-of-range tile number.