Added missed DROP privilege check on the original table for RENAME TABLE command.


mysql-test/r/grant.result:
  Fix for bug #27515: DROP previlege is not required anymore for RENAME TABLE
    - test result.
mysql-test/t/grant.test:
  Fix for bug #27515: DROP previlege is not required anymore for RENAME TABLE
    - test case.
sql/sql_parse.cc:
  Fix for bug #27515: DROP previlege is not required anymore for RENAME TABLE
    - added DROP privilege check on the original table for RENAME TABLE command.