more PSVI

thx goes to MohamedZ for pointing out the current WG debate as I had
my own PSVI questions.

a few ruminations on PSVI;

* what if we want to preserve PSVI annotations through a step that
does not require it ? e.g. something like a psvi-passthru attribute
though perhaps all this is a bit cumbersome for corner case?

* what happens when p:xslt is using a validating XSLT v2.0 does the
existing psvi-required attribute need to be set to true then ?

regards, Jim Fuller