When view column aliased in subselect alias is set on ref which represents
field. When tmp table is created for subselect, it takes name of original field
not ref. Because of this alias on view column in subselect is lost. Which
results in reported error.

Now when alias is set on ref, it's set on ref real item too.


mysql-test/r/view.result:
  Test case for bug #12993  View column rename broken in subselect
mysql-test/t/view.test:
  Test case for bug #12993  View column rename broken in subselect
sql/sql_base.cc:
  Fix bug #12993 View column rename broken in subselect
  Now when alias is set on ref, it's set on ref real item too.