[xslt-conformance] Mapping of issues to questions raised in matrix

[David Marston/Cambridge/IBM <david_marston@us.ibm.com>]

I just realized that the tests I'm citing in my issue reports should
be tied in with the ones that were questioned by test reviewers.

The question about numbering21 is the level="any" case which I
described by reference to numbering61. Also related are
numbering18, numbering29, numbering49, numbering61, numbering69,
and others.

Test numbering22 has a from attribute just to try that combination
of factors. Compare it to numbering52.

Carmelo has a question about numbering58, but I think the answer is
just about mod, not about xsl:number. I wasn't going to propose an
issue on it.

Test numbering64 raises the "nothing matched from" issue in a way
that's similar to numbering19, both being about level="multiple".
.................David Marston