Clarify that ttp:profile@combine and ttp:[*]ProfileCombination are the same.

[nigelmegitt]

There are currently two ways to define the combination of profiles:

1. The profile element's @combine attribute.
2. The tt element's @ttp:processorProfileCombination and @ttp:contentProfileCombination attributes.

The value sets of all three attributes are the same modulo #1028 and the combination algorithms are the same regardless of which source of "combine" semantics is applicable.

However the treatment of that combination semantic in the specification is in text in the section on the profile element and in a helpful table in each of @contentProfileCombination and @processorProfileCombination (and those tables are different because "prohibited" is not allowed in a processor profile but is allowed in a content profile).

It would be helpful to clarify that those tables are in fact the result of applying the combination logic specified in prose under profile element, and maybe move the tables under that prose and reference them from the @...ProfileCombination attribute sections.