(comstr, buy, check_market, display_mark, reset, sell): Change comstr

(comstr, buy, check_market, display_mark, reset, sell): Change comstr
member com_type from mnemo character to item type.
(whichitem): Unused, remove.

(check_market): Use full item name instead of mnemo in telegrams.

(display_mark): Separate arguments for item type and cheapest only.
Cheapest only of specific item type is not implemented.

(rese): Guard against bad com_type.  Delete some code that had no
effect.