mysql-test/r/partition_order.result:
  Changed a test case to handle ordered index scan reverse order as well
mysql-test/t/partition_order.test:
  Changed a test case to handle ordered index scan reverse order as well
sql/ha_myisam.cc:
  More debug info
sql/ha_partition.cc:
  Introduced partition_index_read_last to ensure we use index_read_last in those
  cases towards underlying handler.
  Ensured that index_read with HA_READ_PREFIX_LAST, HA_READ_PREFIX_LAST_OR_PREV and
  HA_READ_BEFORE_KEY uses ordered index scan in reverse order.
sql/ha_partition.h:
  Introduced partition_index_read_last to ensure we use index_read_last in those
  cases towards underlying handler.
  Ensured that index_read with HA_READ_PREFIX_LAST, HA_READ_PREFIX_LAST_OR_PREV and
  HA_READ_BEFORE_KEY uses ordered index scan in reverse order.