of subqueries:

- Extend the grammar rule for 'table_alias' to let it also
  refer an outer table if such exists in our current scope.

- As outer-column refs now will be part of the normal rule
  for producing an 'int_column' or 'char_column' (See above change)
  the special handling of outer table correlations in 'where_clause'
  could be removed.

- Rename 'correlate_iff_subquery' to reflect it is now unused.

- Rename the grammar rule 'outer_join_pattern' to reflect that it
  is unused. (Likely never was, but still want to keep it.)