Problem: getting an autoincrement value for a partition table in the ::info() method we call
the get_auto_increment() for all partitions. That may cause a problem for at least MyISAM
tables that rely on some table state (in this particular case table->naxt_nuber_field is 
set to 0 in the mysql_insert() and we get a crash). 
Moreover, calling get_auto_increment() is superfluous there.

Fix: use ::info(HA_STATUS_AUTO) calls to get autoincrement values for partitions instead of
get_auto_increment() ones in the ha_partition::info().


mysql-test/r/partition.result:
  Fix for bug #28806: Running SHOW TABLE STATUS during high INSERT load crashes server
    - test result.
mysql-test/t/partition.test:
  Fix for bug #28806: Running SHOW TABLE STATUS during high INSERT load crashes server
    - test case.
sql/ha_partition.cc:
  Fix for bug #28806: Running SHOW TABLE STATUS during high INSERT load crashes server
    - use info(HA_STATUS_AUTO) calls to get autoincrement values for partitions,
      set the auto_increment_value as the biggest one.