fix typo and add REE to comment

Author: nurse

ext/mysql2/statement.c

@@ -238,8 +238,8 @@ static int my_big2ll(VALUE bignum, LONG_LONG *ptr)
 #elif defined(HAVE_RB_BIG_CMP)
         rb_big_cmp(bignum, LL2NUM(LLONG_MIN)) == INT2FIX(-1)
 #else
-        /* Ruby 1.8.7 doesn't have rb_big_cmp */
-        rb_funcall(bignum, intern_cmp, 1, LL2NUM(LLONG_MIN)) == INT2FIX(-1)
+        /* Ruby 1.8.7 and REE doesn't have rb_big_cmp */
+        rb_funcall(bignum, id_cmp, 1, LL2NUM(LLONG_MIN)) == INT2FIX(-1)
 #endif
        ) {
       goto overflow;