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

third_party/clipper/README.md

@@ -0,0 +1,5 @@
+Clipper 5.1.6, Angus Johnson, 18 May 2013.
+
+Copied from the existing local `luapower-all-master/csrc/clipper` checkout.
+The source and header are unchanged; see `LICENSE` for the Boost Software
+License. Used for the native terrain's negative powder-contour offset.