[sv-cc] DPI unions as parameters

There is a new Mantis item, #1322, which details problems with various
species of 
unions as DPI parameters.
 
Most of discussion appears as a Bugnote, where some wrap-around effects
make
the text hard to follow.
 
I deliberately haven't prepared a proposal, since 
. that presupposes the outcome of our discussion,
. the actual text changes may be less work than deciding what's best to
do.
 
Ralph Duncan