Objects of the class Item_equal contain an auxiliary member
eval_item of the type cmp_item that is used only for direct 
evaluation of multiple equalities. Currently a multiple equality
is evaluated directly only in the cases when the equality holds
at most for one row in the result set.
The compare collation of eval_item was determined incorectly.
It could lead to returning incorrect results for some queries.


mysql-test/r/join_outer.result:
  Added a test case for bug #26017.
mysql-test/t/join_outer.test:
  Added a test case for bug #26017.
sql/item_cmpfunc.cc:
  Fixed bug #26017.
  Objects of the class Item_equal contain an auxiliary member
  eval_item of the type cmp_item that is used only for direct 
  evaluation of multiple equalities. Currently a multiple equality
  is evaluated directly only in the cases when the equality holds
  at most for one row in the result set.
  The compare collation of eval_item was determined incorrectly.
  It could lead to returning incorrect results for some queries.
sql/item_cmpfunc.h:
  Fixed bug #26017.
  Removed the cmp_collation member from the Item_equal class as useless
  for the current implementation of the class.