Support null values in proc relational joins

Defect Tracker #24719: For dependent procedure executions to support null values we need to support criteria of the form:

(value is not null and input = value) or (value is null and input is null)

Currently this will not plan correctly because we do not recognize that the halfs of the conjunct are mutually exclusive and will not require 'or' support if the value is a reference and will have a known value.