The problem was due to the fact that with --lower-case-table-names set to 1 
the function find_field_in_group did not convert the prefix 'HU' in
HU.PROJ.CITY into lower case when looking for it in the group list. Yet the
names in the group list were extended by the database name in lower case.


mysql-test/r/having.result:
  Added a test case for bug #15917.
mysql-test/t/having.test:
  Added a test case for bug #15917.
sql/item.cc:
  Fixed bug #15917: unexpected complain for a NIST test case.
  The problem was due to the fact that with --lower-case-table-names set to 1 
  the function find_field_in_group did not convert the prefix 'HU' in
  HU.PROJ.CITY into lower case when looking for it in the group list. Yet the
  names in the group list were extended by the database name in lower case.
  The needed conversion was added to the code of find_field_in_group.