/* ============================================================================
=head1 Allocation and deallocation of SVs.
+
An SV (or AV, HV, etc.) is allocated in two parts: the head (struct
sv, av, hv...) contains type and reference count information, and for
many types, a pointer to the body (struct xrv, xpv, xpviv...), which
are decremented to point at the unused 'ghost' memory, knowing that
the pointers are used with offsets to the real memory.
-=cut
-
Allocation of SV-bodies is similar to SV-heads, differing as follows;
the allocation mechanism is used for many body types, so is somewhat
more complicated, it uses arena-sets, and has no need for still-live