* bus/bus.c: (bus_context_reload_config): Flush the user database cache on

  * bus/bus.c: (bus_context_reload_config): Flush the user database cache on
   config reload.
   * bus/dbus-daemon.1.in: Also note that SIGHUP flushes the user/group
   information caches
   * dbus/dbus-hash.c: (_dbus_hash_table_remove_all):
   * dbus/dbus-hash.h: Add function to remove all entries from a hash table
   * dbus/dbus-userdb.c: (_dbus_user_database_flush):
   * dbus/dbus-userdb.h: Add function to flush all user/group information
   caches.