[perl #87708] $tied % $tied and $tied * $tied under use integer

[perl #87708] $tied % $tied and $tied * $tied under use integer

This is just part of #87708.

This fixes the % and * operators under ‘use integer’ when the same
tied scalar is used for both operands and returns two different val-
ues. Before this commit, get-magic would be called only once and
the same value used. In 5.12.x * just worked but the operands were
swapped for %.

It turns out that every operator using the dPOPTOPiirl_nomg macro
needs exactly the same treatment, so this commit eliminates the
dPOPTOPiirl_halfmg macro added a few commits ago and modifies
dPOPTOPiirl_nomg to do was it was doing. This should be perfectly
safe, as dPOPTOPiirl_nomg has not been in a stable release (and is
only for internal use anyway).