Build modes

I do not know what I was doing:

NULL checks

building without BLUA support

functions that do not depend on outside vars should be tagged with "const", AKA, FUNCMATH

src/blua/lvm.c

@@ -732,7 +732,8 @@ void luaV_execute (lua_State *L, int nexeccalls) {
luaG_runerror(L, LUA_QL("for") " limit must be a number");
else if (!tonumber(pstep, ra+2))
luaG_runerror(L, LUA_QL("for") " step must be a number");
-        setnvalue(ra, luai_numsub(nvalue(ra), nvalue(pstep)));
+        if (ra && pstep)
+          setnvalue(ra, luai_numsub(nvalue(ra), nvalue(pstep)));
dojump(L, pc, GETARG_sBx(i));
continue;
}