higher resolution for waterlevel

Interpret the waterlevel value as tenths of a cube.

This makes the waterlevel variable a float value to the user, while the
map file still stores an integer value - but now it is interpreted
differently - for example, a waterlevel value of 123 now means 12.3 cubes
instead of 123. Old map files are converted during loading.

Note: the values of waterlevel and hdr.waterlevel need to be in sync.

DOCREF waterlevel

source/src/bot/bot_ai.cpp

@@ -1744,7 +1744,7 @@ bool CBot::WaterNav()
 
                 if (UnderWater(v)) continue; // Skip, cube is underwater
 
-                if (hdr.waterlevel < (v.z - 2.0f)) continue; // Cube is too high
+                if (waterlevel < (v.z - 2.0f)) continue; // Cube is too high
 
                 // Check if the bot 'can fit' on the cube(no near obstacles)
                 bool small_ = false;