Phase 4 (final): Remove associated stored procedures when a database is dropped.


mysql-test/r/sp-security.result:
  drop database now deletes associated SPs.
mysql-test/r/sp.result:
  drop database now deletes associated SPs.
mysql-test/t/sp-security.test:
  drop database now deletes associated SPs.
mysql-test/t/sp.test:
  drop database now deletes associated SPs.
sql/sp.cc:
  New function for deleting all SPs associated with a database.
sql/sp.h:
  New function for deleting all SPs associated with a database.
sql/sp_cache.cc:
  New function for just invalidating all SP caches (when dropping a database).
sql/sp_cache.h:
  New function for just invalidating all SP caches (when dropping a database).
sql/sql_db.cc:
  When dropping a database, also delete all associated SPs.