Lot of bugfixes

* Adding clipper to generate the terrain's negative powder-contour offset.
* Fixing RDB issues (fracture, active trigger, performances)
* Fixing blood emission
* Fixing the freezing formula on liquids
* Fixing Steve spawning due to a missed test.
* Reaction table properly build

shaders/particle_alloc.glsl

@@ -0,0 +1,16 @@
+int alloc_part() {
+    const uint s0 = atomicAdd(fcnt[1], 1u);
+    for (uint k = 0u; k < 64u; ++k) {
+        const uint s = (s0 + k) % uint(FPART_MAX);
+        const uint word = 4u + uint(FP_MAX) * 24u + s * 12u + 4u;
+        const uint previous = atomicAdd(fxwords[word], 0u);
+        if (uintBitsToFloat(previous) <= 0.0 && atomicCompSwap(fxwords[word], previous, floatBitsToUint(3.0e38)) == previous) return int(s);
+    }
+    return -1;
+}
+
+void release_part(uint slot) {
+    // Publish a free slot only after its previous owner has finished all writes.
+    memoryBarrierBuffer();
+    atomicExchange(fxwords[4u + uint(FP_MAX) * 24u + slot * 12u + 4u], 0u);
+}