Problem: commit doesn't delete savepoints if there are no changes 
in the transaction.

Fix: delete them in such cases.


mysql-test/r/innodb_mysql.result:
  Fix for bug #26288: savepoint not deleted, comit on empty transaction
    - test result.
mysql-test/t/innodb_mysql.test:
  Fix for bug #26288: savepoint not deleted, comit on empty transaction
    - test case.
sql/handler.cc:
  Fix for bug #26288: savepoint not deleted, comit on empty transaction
    - call transaction.cleanup() even if nht is 0 to delete 
  possible savepoints.