pad.h: PADNAME_SV

pad.h: PADNAME_SV

If CPAN modules should not assume that pad names are SVs, we need
to provide a better way than newSVpvn(PADNAME_PV(pn),PADNAME_LEN(pn))
to get an SV out of it, as, knowing that pad names are just SVs, the
core can do it more efficiently by simply returning the pad name
itself.