When a view was used inside a trigger or a function, lock type for
tables used in a view was always set to READ (thus making the view
non-updatable), even if we were trying to update the view.

The solution is to set lock type properly.


mysql-test/r/view.result:
  Add result for bug#17591: Updatable view not possible with trigger
  or stored function.
mysql-test/t/view.test:
  Add test case for bug#17591: Updatable view not possible with trigger
  or stored function.
sql/sql_view.cc:
  Move the code that sets requested lock type before the point where
  we exit from mysql_make_view() when we process a placeholder for
  prelocked table.