Bug fixes & misc:
- Follow up 7fd6776, correcting how to make player sit by autotrade persistance.
- Follow up 7fd6776, pc_setstand() does a check if player can stand or not.
- bugreport:9174, buyingstore_close() doesn't clear buyingstores data on table.
- Fixed "missing" buyingstore search (purchase type search) in searchstore, by adding DBMap *buyingstore_db.
- Added nullpo checks on some buyingstore.c functions.
- Added do_init_buyingstore() and do_final_buyingstore().
- Failing autotrader from pc_setpos(). (Since autotrade doesn't have 'fd'? FIXME later)

Signed-off-by: Cydh Ramdh <house.bad@gmail.com>