will call handler::position() during key scan. 
Undo the previous, less efficient fix (cset 2004-11-30 19:56:25+02:00, heikki@hundin.mysql.fi)


innobase/include/row0mysql.h:
  undo cset 1.1698.1.2
sql/ha_innodb.cc:
  undo cset 1.1698.1.2
sql/opt_range.cc:
  Make index_merge code call file->extra(HA_EXTRA_RETRIEVE_PRIMARY_KEY) if file->position() will be called.
  Also fixed a typo and added a couple of error checks.