creation of the partitioned table could fail as we created Item-s for
it's list function in thd->mem_root, and then do Item->fix_fields
in the context of other table->mem_root (so that memory alloced
there was alloced in this table->mem_root). As we freed the
table->mem_root before we do thd->free_items, our Item-s had
pointers to the freed memory, that caused the crash


mysql-test/r/partition.result:
  result
mysql-test/t/partition.test:
  testcase
sql/item_cmpfunc.cc:
  here is better place for the implementation
sql/item_cmpfunc.h:
  implementation moved to .cc file
sql/sql_partition.cc:
  work_part_info_used parameter added to mysql_unpack_partition
sql/sql_partition.h:
  work_part_info_used parameter added to mysql_unpack_partition
sql/table.cc:
  we do 'fix_partition_func' using the proper arena now.
  It's necessary as Item_*::fix_fields can alloc memory
  using thd->mem_root and this has to be same mem_root that
  we used to alloc these Item-s