Properly export all lua-facing functions and use those for initialization (love.cpp no longer explicitly mentions implementations)

src/modules/physics/box2d/wrap_PrismaticJoint.h

@@ -50,7 +50,7 @@ namespace box2d
 	int w_PrismaticJoint_getLowerLimit(lua_State * L);
 	int w_PrismaticJoint_getUpperLimit(lua_State * L);
 	int w_PrismaticJoint_getLimits(lua_State * L);
-	int luaopen_prismaticjoint(lua_State * L);
+	extern "C" int luaopen_prismaticjoint(lua_State * L);
 
 } // box2d
 } // physics