Fixed bug #11088: a crash for queries with GROUP BY a BLOB column
  + COUNT(DISTINCT...) due to an attempt to allocate a too large
  buffer for the BLOB field.
  Now the size of the buffer is limited by max_sort_length.
group_by.test, group_by.result:
  Added a test case for bug #11088.


mysql-test/r/group_by.result:
  Added a test case for bug #11088.
mysql-test/t/group_by.test:
  Added a test case for bug #11088.
sql/item.h:
  Fixed bug #11088: a crash for queries with GROUP BY a BLOB column
  + COUNT(DISTINCT...) due to an attempt to allocate a too large
  buffer for the BLOB fields.
  Now the size of the buffer is limited by max_sort_length.
sql/item_buff.cc:
  Fixed bug #11088: a crash for queries with GROUP BY a BLOB column
  + COUNT(DISTINCT...) due to an attempt to allocate a too large
  buffer for the BLOB fields.
  Now the size of the buffer is limited by max_sort_length.
sql/sql_select.cc:
  Fixed bug #11088: a crash for queries with GROUP BY a BLOB column
  + COUNT(DISTINCT...) due to an attempt to allocate a too large
  buffer for the BLOB fields.
  Now the size of the buffer is limited by max_sort_length.