tasks for different handlers.  Add a callback from berkeley db to
delete log files that are no longer needed.


configure.in:
  enable berkeley dbugging when --with-debug is on
sql/Makefile.am:
  change handle_flush to a general maintenance manager thread
sql/mysql_priv.h:
  change handle_flush to a general maintenance manager thread
sql/mysqld.cc:
  change handle_flush to a general maintenance manager thread
sql/ha_berkeley.cc:
  add callback to delete unneeded log files