Remove dflt_field from field structure as this was only needed when createing temporary table and I found another soultion that doesn't increase the size of the field structure for all table instances. (Better fix for bug #19089)
Fixed compiler warnings
Fixed valgrind warning in Item_date_add_intervall::eq. (Recoding of bugfix #19490)


sql/field.cc:
  remove dflt_field from field structure (not needed)
  Simple cleanup of code that been copied elsewhere
sql/field.h:
  remove dflt_field from field structure (not needed)
sql/item.h:
  Removed compiler warnings
sql/item_timefunc.cc:
  Fixed Item_date_add_intervall::eq
  The problem was that when we call 'eq' 'this' is not fixed, which means we can't call const_item() or a value function.
  I fixed this so that we check eq for all arguments and that the sign and type are identical.
  (The original code gave a 'accessing uninitialized data' in valgrind.
sql/mysql_priv.h:
  Added default fields to create_tmp_field
sql/sql_insert.cc:
  New default_field parameter to create_tmp_field()
sql/sql_select.cc:
  New default_field parameter to create_tmp_field()
  Use this in create_tmp_table() to set right default value for a field