build.xml: begin work on version 1.7

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@882 d9718cc8-9f43-0410-858b-315f434eb58c
tiles.rc: ensure that invisible open-drawbridge tiles do not burn

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@883 d9718cc8-9f43-0410-858b-315f434eb58c
tiles.rc: tag which road/wire/rail tiles are "over water"

"over water" means when they decay or are bulldozed, they are replaced
with water instead of rubble/dirt.

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@884 d9718cc8-9f43-0410-858b-315f434eb58c
tiles.rc: rewrite isOverWater() to use the new "over water" attribute

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@885 d9718cc8-9f43-0410-858b-315f434eb58c
make-tiles: allow tile specification to be empty

this fixes a build-crash bug if a tile is not given any images

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@886 d9718cc8-9f43-0410-858b-315f434eb58c
tiles.rc: remove tile information for 7 unused tile numbers (amongst roads tiles)

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@887 d9718cc8-9f43-0410-858b-315f434eb58c