Added a test for bug #8615.
sql_select.cc:
  Fixed bug #8615.
  This fix only removed the cause of the reported crash.
  It does not resolve other problems of rollup queries
  with DISTINCT. They were fixed in the previous patch 
  for bug 8616.


sql/sql_select.cc:
  Fixed bug #8615.
  This fix only removed the cause of the reported crash.
  It does not resolve other problems of rollup queries
  with DISTINCT. They were fixed in the previous patch 
  for bug 8616.
mysql-test/t/olap.test:
  Added a test for bug #8615.
mysql-test/r/olap.result:
  Added a test for bug #8615.