Each platform's implementation of askappend() is no longer required

Each platform's implementation of askappend() is no longer required
to consult cfg.logxfovr, because it gets done once in logging.c.
askappend() is now called only when a question _really_ needs to be
asked of the user. Also in this checkin, cleanup_exit() in console.c
no longer consults cfg.protocol to decide whether to save the random
seed, because random_save_seed() can make that decision for itself
and do it better.

git-svn-id: http://svn.tartarus.org/sgt/putty@2552 cda61777-01e9-0310-a592-d414129be87e