Better emulation correct SELECT tree for fields expressions of merging view during name resolving (BUG#6394)


mysql-test/r/view.result:
  added test with subquery in the FROM clause
mysql-test/t/view.test:
  added test with subquery in the FROM clause
sql/table.cc:
  use SELECT in which view is merging as main SELECT for nameresolving to make correct support for subqueries in the view.