ALL EDITORS V437 - EACH ACCOUNT ONLY SEES, IMPORTS AND EXPORTS ITS OWN CHARACTERS
(V436 base: campaign join kept; V435 account folders on Import/Export kept)

INSTALL
  Close every BG2 window, run All Editors\SETUP_IN_GAME_ACCOUNTS.bat.

WHAT WAS WRONG
  Both BG2 windows share ONE characters\ folder. Opening Import/Export
  renames <account>\ to characters\ (one account at a time), but:
  - the second window's login was refused by the router ("another account
    is using this shared characters folder"), so its folder could never be
    opened, and
  - OPEN unlocked anyway after 0.8 s even without the router's answer, so
    the second window could see, import or export into whatever was in
    characters\ at that moment (the other account's characters, or the
    shared root).

V437
  - Every account folder has an owner file: _DRAKOWNER_<account>.txt
    (written by setup, login and every Import/Export opening).
  - Import / Export (record screen and character creation) open ONLY when
    BG2 itself sees YOUR owner file in characters\ (Infinity_GetFileExists),
    or the router confirms your folder. No blind time-based unlock.
  - If the other account has Import/Export open, you get:
      "Another player is using Import/Export. <you>'s characters open as
       soon as they close it..."   (CANCEL / RETRY / OPEN)
    The request is repeated every 2 s; OPEN lights up when characters\ is
    yours.
  - Import Done, Export Done and character-creation Export Done refuse to
    read/write if characters\ is not (or no longer) your folder.
  - After your panel closes, the release is repeated every 3 s until your
    folder has really left characters\ (up to 2 minutes), so the other
    window is never blocked by a lost message.
  - Several accounts may now be logged in at the same time (one per BG2
    window). Only one account folder is characters\ at any moment.
  - A window that crashes or closes with a panel open gives its folder back
    (exit watcher), the other window can continue.

UNCHANGED
  Campaign join (V436), JOIN GAME, Resume, account folders, .CHR names.

CHECKS
  python -m unittest test_v437_character_isolation test_v435_import_export_mount test_v436_campaign_join -v
NOT TESTED HERE: the real BG2 executable (Infinity_GetFileExists on home:/
paths is used by stock BG2 for install:/ paths; if home:/ is not supported
the absolute profile path from DRAKREN.lua is used).
