The name resolution for correlated subqueries and HAVING clauses
failed to distinguish which of two was being performed when there 
was a reference to an outer aliased field.
Fixed by adding the condition that HAVING clause name resulotion
is being performed.


mysql-test/r/group_by.result:
  Bug#31797: Test result
mysql-test/t/group_by.test:
  Bug#31797: Test case
sql/item.cc:
  Bug#31797: 
  Corrected function comment.
  The fix, raising the error is restricted to HAVING name resolution.