[RDY] Convert some values into bools

Not a very exciting change. 
@ZyX-I Also you may not have seen via email, elsewhere in this PR in buffer_defs.h:

    int b_changed

was changed to

    bool b_changed

---

@war1025 I looked around and found in fileio.c: `save_changed` is an uninitialized `int` that is later assigned b_changed. `save_changed` can be easily changed to bool, can you add it to this PR?