Ensure that raid_chunks is not set to higher than 255 as this could cause problems with DROP DATABASE. (Bug #3182)


mysql-test/r/raid.result:
  Test of raid_chunks > 255
mysql-test/t/raid.test:
  Test of raid_chunks > 255
sql/item.cc:
  Fixed wrong usage of str_value in Item::save_in_field
  This could caused a stack overrun with some very special INSERT ... SELECT ... GROUP BY queries where the GROUP BY value was an expression that generated a NULL value. (Bug #3265)
  The Item_copy_string::save_in_field() function is from 4.1 and helps optimized this case a bit
sql/item.h:
  Fixed wrong usage of str_value in Item_copy_string::save_in_field
sql/sql_insert.cc:
  More debug information
sql/table.cc:
  Ensure that raid_chunks is not set to higher than 255 as this could cause problems with DROP DATABASE.
  Another problem with values > 255 is that in the .frm file we store the chunks value in one byte.
  (Bug #3182)