* Fixed test results.


mysql-test/r/index_merge_ror.result:
  Typo fix
mysql-test/r/rowid_order_bdb.result:
  new index_merge EXPLAIN output format changes
mysql-test/r/rowid_order_innodb.result:
  new index_merge EXPLAIN output format changes
sql/opt_range.cc:
  Undo of previous fix:
  If cost(full_scan_on_covering_index) < cost(best_range_scan) <  cost(full_table_scan) 
  use full_scan_on_covering_index, not best_range_scan.
  The fix affects read plan choice for more queries then initially anticipated, so I'm reverting it for now, will get back to this later