[ Post-Rapperswil ]

The following update is a result of the discussion during the Rapperswil meeting, the P/R expresses all comparisons by delegating to sub_match's compare functions. The processing is rather mechanical: Only == and < where defined by referring to sub_match's compare function, all remaining ones where replaced by the canonical definitions in terms of these two.

Moved to Tentatively Ready after 5 positive votes on c++std-lib.