able delay_key_write as default (as it was in 4.0.2)


Docs/manual.texi:
  Updated information about variable DELAY_KEY_WRITE.
mysql-test/r/type_decimal.result:
  Updated results
mysql-test/r/variables.result:
  Updated results
mysql-test/t/type_decimal.test:
  Fixed test to not cause purify error in mathlib during purify.
mysql-test/t/variables.test:
  Test new usage of DELAY_KEY_WRITE
sql/ha_innodb.cc:
  Merge with 3.23 code
sql/mysql_priv.h:
  Changed SQL variable delay_key_write to an enum
sql/mysqld.cc:
  Changed SQL variable delay_key_write to an enum.
  Enable delay_key_write as default (as it was in 4.0.2)
sql/set_var.cc:
  Changed SQL variable delay_key_write to an enum
sql/set_var.h:
  Changed SQL variable delay_key_write to an enum
sql/sql_class.h:
  Changed SQL variable delay_key_write to an enum
sql/sql_yacc.yy:
  Changed SQL variable delay_key_write to an enum