new EXPLAIN parameter to show real query as it was interpreted
(SCRUM) (WL#1274)


mysql-test/r/subselect.result:
  new explains
mysql-test/r/union.result:
  new explains
mysql-test/t/subselect.test:
  new explains
mysql-test/t/union.test:
  new explains
sql/item.cc:
  fixed printability of Items in SELECT list
sql/item.h:
  fixed printability of Items in SELECT list
sql/item_cmpfunc.cc:
  fixed print()
sql/item_cmpfunc.h:
  fixed print()
sql/item_subselect.cc:
  subqueries made printable
sql/item_subselect.h:
  subqueries made printable
sql/mysql_priv.h:
  union option made looks like options
sql/sql_derived.cc:
  now this link is used
sql/sql_lex.cc:
  subqueries made printable
sql/sql_lex.h:
  subqueries made printable
  new EXPLAIN parameter support
sql/sql_parse.cc:
  new EXPLAIN parameter
sql/sql_select.cc:
  debug output
  new EXPLAIN parameter support
sql/sql_select.h:
  new EXPLAIN parameter support
sql/sql_yacc.yy:
  new EXPLAIN parameter support
  SELECT printability support