Freeze PL_sv_zero properly

[toddr]

No description provided.

[atoomic]

note: PL_Zero is the PV of PL_sv_zero
We probably want to freeze PL_sv_zero in this case

[atoomic]

need to check for other special SVs*

[atoomic]

B::SPECIAL should already take care of these PL_*

[atoomic]

from B

 our @specialsv_name = qw(Nullsv &PL_sv_undef &PL_sv_yes &PL_sv_no
             (SV*)pWARN_ALL (SV*)pWARN_NONE (SV*)pWARN_STD
                         &PL_sv_zero);

[atoomic]

idea: check for common PVs strings when generating a COWPV
and die or warn on generic PVX like Zero, Yes, No...
as this is either an indication we are not using the global PL_sv* or that we should use the PVX from it