Outer joins cleanup: Remove TABLE::outer_join and use TABLE::maybe_null only (2nd patch after Monty's comments).


sql/mysql_priv.h:
  Outer joins cleanup: Remove TABLE::outer_join and use TABLE::maybe_null only.
sql/opt_range.cc:
  Outer joins cleanup: Remove TABLE::outer_join and use TABLE::maybe_null only.
sql/sql_base.cc:
  Outer joins cleanup: Remove TABLE::outer_join and use TABLE::maybe_null only.
sql/sql_select.cc:
  Outer joins cleanup: Remove TABLE::outer_join and use TABLE::maybe_null only.
sql/table.h:
  Outer joins cleanup: 
   * Remove TABLE::outer_join and use TABLE::maybe_null only.
   * Added comments.