DDS15 — Missing APIs for (read|take)_instance_w_condition

For keyed topics, the core set of read or take APIs support read|take, read|take_instance, and read|take_next_instance.

The corresponding set of API's for read or take with conditions only specified read|take_w_condition and read|take_next_instance_w_condition. The specification lacks the APIs for read|take_instance_w_condition.

Lack of these APIs deprives the user from the ability to read or take from a specific instance while limiting the sample set to specific conditions.