The convert_constant_item() function converts constant items to ints on
prepare phase to optimize execution speed. In this case it tries to evaluate
subselect which contains a derived table and is contained in a derived table. 
All derived tables are filled only after all derived tables are prepared.
So evaluation of subselect with derived table at the prepare phase will
return a wrong result.

A new flag with_subselect is added to the Item class. It indicates that
expression which this item represents is a subselect or contains a subselect.
It is set to 0 by default. It is set to 1 in the Item_subselect constructor
for subselects.
For Item_func and Item_cond derived classes it is set after fixing any argument
in Item_func::fix_fields() and Item_cond::fix_fields accordingly.
The convert_constant_item() function now doesn't convert a constant item
if the with_subselect flag set in it. 


mysql-test/t/view.test:
  Added test case for bug#19077: A nested materialized derived table is used before being populated.
mysql-test/t/subselect.test:
  Added test case for bug#19077: A nested materialized derived table is used before being populated.
mysql-test/r/view.result:
  Added test case for bug#19077: A nested materialized derived table is used before being populated.
mysql-test/r/subselect.result:
  Added test case for bug#19077: A nested materialized derived table is used before being populated.
sql/item_subselect.cc:
  Fixed bug#19077: A nested materialized derived table is used before being populated.
  The Item_subselect class constructor sets new with_subselect flag to 1.
sql/item_func.cc:
  Fixed bug#19077: A nested materialized derived table is used before being populated.
  
  The Item_func::fix_fields() sets new with_subselect flag from with_subselect flags of its arguments.
sql/item_cmpfunc.cc:
  Fixed bug#19077: A nested materialized derived table is used before being populated.
  The convert_constant_item() function now doesn't convert a constant item
  with the with_subselect flag set.
  The Item_cond::fix_fields() sets new with_subselect flag from with_subselect flags of its arguments.
sql/item.cc:
  Fixed bug#19077: A nested materialized derived table is used before being populated.
  Set new with_subselect flag to default value - 0 in the Item constructor.
sql/item.h:
  Fixed bug#19077: A nested materialized derived table is used before being populated.
  A new flag with_subselect is added to the Item class. It indicates that
  expression which this item represents is a subselect or contains a subselect.
  It is set to 0 by default.