Original commentary:

Bug #37348: Crash in or immediately after JOIN::make_sum_func_list
            
The optimizer pulls up aggregate functions which should be aggregated in
an outer select. At some point it may substitute such a function for a field
in the temporary table. The setup_copy_fields function doesn't take this
into account and may overrun the copy_field buffer.
            
Fixed by filtering out the fields referenced through the specialized
reference for aggregates (Item_aggregate_ref).
Added an assertion to make sure bugs that cause similar discrepancy 
don't go undetected.


mysql-test/r/func_group.result:
  Backport bug #37348 fix 5.1 --> 5.0.
mysql-test/t/func_group.test:
  Backport bug #37348 fix 5.1 --> 5.0.
sql/item.cc:
  Backport bug #37348 fix 5.1 --> 5.0.
sql/item.h:
  Backport bug #37348 fix 5.1 --> 5.0.
sql/sql_select.cc:
  Backport bug #37348 fix 5.1 --> 5.0.