- fixed a problem with RIGHT JOIN ON and enabled corresponding tests in select.test
- fixed a memory leak


mysql-test/r/select.result:
  Fixed a problem with RIGHT JOIN ON queries, enabling the corresponding tests.
mysql-test/t/select.test:
  Fixed a problem with RIGHT JOIN ON queries, enabling the corresponding tests.
sql/sql_base.cc:
  Fixed a problem with RIGHT JOINs that have operand(s) which are NATURAL JOIN(s).
sql/table.h:
  Inherit from Sql_alloc for proper memory allocation.
  The change fixes a memory leak.