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.)

llex.c

@@ -136,7 +136,7 @@ TString *luaX_newstring (LexState *ls, const char *str, size_t l) {
   if (isempty(o)) {  /* not in use yet? */
     /* boolean value does not need GC barrier;
        table is not a metatable, so it does not need to invalidate cache */
-    setbvalue(o, 1);  /* t[string] = true */
+    setbtvalue(o);  /* t[string] = true */
     luaC_checkGC(L);
   }
   else {  /* string already present */