Test case for a #2996 bug fix
multi_update.test:
  test case for a #2996 bug fix
sql_select.cc:
  Fix for a bug #2996 involving multi-table updates over the const tables


sql/sql_select.cc:
  Fix for a bug #2996 involving multi-table updates over the const tables
mysql-test/t/multi_update.test:
  test case for a #2996 bug fix
mysql-test/r/multi_update.result:
  Test case for a #2996 bug fix