PDL::Core::pdumphash mutates ndarrays

[mohawk2]

This reproduces:

my $x = sequence 3; $x->doflow; my $y = $x + 1;
isnt $y->trans_parent, undef, '$y has parent';
isnt PDL::Core::pdumphash($x), undef, 'pdumphash works';
isnt $y->trans_parent, undef, '$y still has parent after pdumphash';

The cause of this, identified using:

make core && perl -Mblib -MPDL -e '$|=1; PDL::Core::set_debugging(1);
  $x = sequence 3; $x->doflow; $y = $x + 1;
  print "BEFORE\n"; $_->dump for $x, $y;
  PDL::Core::pdumphash($x); ' |perl Example/address-pseudonymise |&less

is almost certainly that the intermediate ndarray created in the addition above gets attached to an SV which is returned by $trans->parent. This SV then gets destroyed, which then makes the ndarray look like it's not needed (it had an SV which has now gone away), so it gets destroyed.

[mohawk2]

This was fixed by adding a state flag when attaching an SV to pdls that didn't have one before, in Core.xs. That was then detected and reversed in DESTROY, without then carrying on to do pdl_destroy.