Make map::draw use tripoint internally
Make map::drawsq draw based on 3D surrounding.

added map::blocks_vertical_view_down and map::blocks_vertical_view_up to check if one can see through the floor / roof of a tile

add terrain flag TFLAG_NOFLOOR (indicates one can see vertical through the floor)

new rl_dist(tripoint,tripoint) is equal to the other rl_dist functions, it ignores the z-component