cleanup: reduce visibility of many of the named tiles

(no reason that the front-end needs to reference these tiles directly)

git-svn-id: http://micropolis.googlecode.com/svn/trunk@855 d9718cc8-9f43-0410-858b-315f434eb58c
cleanup: remove unused constant: UNUSED_TRASH2

git-svn-id: http://micropolis.googlecode.com/svn/trunk@856 d9718cc8-9f43-0410-858b-315f434eb58c
cleanup: remove two more unused tile constants

git-svn-id: http://micropolis.googlecode.com/svn/trunk@857 d9718cc8-9f43-0410-858b-315f434eb58c
cleanup: rename FREEZ to RESCLR for consistency

matches the naming pattern used for COMCLR and INDCLR

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