fixed aggregate functions in PS (BUG#3360)


mysql-test/r/union.result:
  4.1 more correct error
sql/item_cmpfunc.h:
  and_conds do not make fix fields
sql/item_sum.cc:
  storing/restoring argument of aggregate function for prepared statements
  restoring order list of group_concat for safety
sql/item_sum.h:
  storing/restoring argument of aggregate function for prepared statements
  layout fix
sql/mysql_priv.h:
  just declaration
sql/sql_base.cc:
  fix_fields() have to be called with temporary memory pool active
sql/sql_parse.cc:
  removed hack with item pointer storing
sql/sql_prepare.cc:
  debug output added
  removed hack with item pointer storing
sql/sql_select.cc:
  fix_fields now should be called separately
sql/sql_union.cc:
  removed wrong merged check from 4.0 (4.1 have its own protection)
sql/table.h:
  removed hack with item pointer storing
tests/client_test.c:
  new test fo PS