Basiland alpha: water that knows where down is

This week's Friday build is the one we have been promising since spring: water
behaves. Pour it at the top of a structure and it finds every gap you left,
which turns out to be a very effective way of reviewing your own architecture.

In this build

• Fluid pass. Water, and the first sketch of lava, flow brick to brick.
• Rails and carts. They obey slope. Carts derail. This is a feature.
• Eight players. Up from four, with no server to rent.
• Paint. Every brick kind takes every colour.

Known and being chased: carts occasionally take a corner they should not, and
very tall towers still round their shadows badly.