We use INT_RESULT type if all arguments are of type INT for 'if', 'case', 
'coalesce' functions regardless of arguments' unsigned flag, so sometimes we can
exceed the INT bounds.


mysql-test/r/select.result:
  Fix for bug #22026: Warning when using IF statement and large unsigned bigint
    - test result.
mysql-test/t/select.test:
  Fix for bug #22026: Warning when using IF statement and large unsigned bigint
    - test case.
sql/item_cmpfunc.cc:
  Fix for bug #22026: Warning when using IF statement and large unsigned bigint
    - take into account unsigned flags aggregating result types:                    
      return INT_RESULT only if two items with INT_RESULT type                      
      have equal unsigned_flags, otherwise return REAL_RESULT.