Remove changes made by bug fix #8147. They strips list of insert_table_list to
only insert table, which results in error reported in bug #9728.
Added flag to Item to resolve ambigous fields reported in bug #8147.


sql/item.h:
  Fix bug#9728  decreased functionality in "on duplicate key update".
sql/item.cc:
  Fix bug#9728  decreased functionality in "on duplicate key update"
sql/sql_parse.cc:
  Fix bug#9728  decreased functionality in "on duplicate key update"
sql/sql_base.cc:
  Fix bug#9728  decreased functionality in "on duplicate key update".
sql/sql_yacc.yy:
  Fix bug#9728  decreased functionality in "on duplicate key update"
mysql-test/t/insert_select.test:
  Test case for bug#9728 Decreased functionality in "on duplicate key update".
mysql-test/r/insert_select.result:
  Test case for bug#9728 Decreased functionality in "on duplicate key update".