xantispam: basic implementation of optionally accpting inventory
offers distinctly by origin and type; involves new rules
"&-InventoryHandleDistinctly" and "AcceptInventory?[type]"
xantispam: fixed return value of xantispam_backgnd() when loading the
chat history into the external editor
code cleanup of inventory_offer_handler() to simplify logic ---
disables xantispam distinct inventory accept features which will be
put back with next commit
xantispam distinct inventory accept put back in after cleanup