Add two new configuration attributes, ds-cfg-enabled-alert-type and
ds-cfg-disabled-alert-type to alert handler configuration entries.  If a set of
enabled alert types is given, then only alerts with one of those types will be
passed to the associated alert handler.  If a set of disabled alert types is
given, then only alerts without one of those types will be passed to the
associated alert handler.  If both enabled and disabled lists are provided,
then only alerts with a type on the enabled list and not on the disabled list
will be processed.

OpenDS Issue Number:  2027