while space allocation

Under some circumstances DISTINCT clause can be converted to grouping.
In such cases grouping is performed by all items in the select list.
If an ORDER clause is present then items from it is prepended to group list.
But the case with ORDER wasn't taken into account when allocating the
array for sum functions. This leads to memory corruption and crash.

The JOIN::alloc_func_list() function now allocates additional space if there
is an ORDER by clause is specified and DISTINCT -> GROUP BY optimization is
possible.


mysql-test/t/select.test:
  Added the test case for bug#20503: Server crash due to the ORDER clause not taken into account while space allocation
mysql-test/r/select.result:
  Added the test case for bug#20503: Server crash due to the ORDER clause not taken into account while space allocation
sql/sql_select.cc:
  Fixed bug#20503: Server crash due to the ORDER clause not taken into account
  while space allocation
  The JOIN::alloc_func_list() function now allocates additional space if there
  is an ORDER by clause is specified and DISTINCT -> GROUP BY optimization is
  possible.