bug #6515: count(distinct...) crashes the server)


mysql-test/r/count_distinct.result:
  A test case (bug #6515: count(distinct...) crashes the server)
mysql-test/r/func_gconcat.result:
  A test case (bug #6475: Another server crash in 5.0.2)
mysql-test/t/count_distinct.test:
  A test case (bug #6515: count(distinct...) crashes the server)
mysql-test/t/func_gconcat.test:
  A test case (bug #6475: Another server crash in 5.0.2)
sql/sql_select.cc:
  A fix (bug #6475: Another server crash in 5.0.2
         bug #6515: count(distinct...) crashes the server)
  In order to prevent repeated setup() call in the JOIN::make_sum_func_list(),
  the code was splitted: new setup_sum_funcs() was introduced.
  Note: we don't call setup_sum_funcs() in the opt_range.cc:get_best_group_min_max().