1) user.number immediately after login() remains zero, but changes
   "sometime" after.  Avoid using user.number right after login()
   call to generate filename.  All data/user/0000.imap files can
   be deleted after this change.
2) Saving Seen data would modify the object storing it when binary
   seen values were used.  Use JSON.parse(JSON.stringify() to make
   a copy before saving and restore it afterward.  Should fix issue
   reported by nickshanks1 over IRC.