Changed internal representation of booleans

Instead of an explicit value (field 'b'), true and false use different
tag variants. This avoids reading an extra field and results in more
direct code. (Most code that uses booleans needs to distinguish between
true and false anyway.)

lapi.c

@@ -574,7 +574,10 @@ LUA_API void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n) {
 
 LUA_API void lua_pushboolean (lua_State *L, int b) {
   lua_lock(L);
-  setbvalue(s2v(L->top), (b != 0));  /* ensure that true is 1 */
+  if (b)
+    setbtvalue(s2v(L->top));
+  else
+    setbfvalue(s2v(L->top));
   api_incr_top(L);
   lua_unlock(L);
 }