Integrate perlio:

Integrate perlio:

[ 14281]
Correct slab allocator for case where sizeof(IV) > sizeof(IV *)
e.g. -Duse64bitint on a 32-bit platform.
Now uses I32 for use-count and is more careful with its casts.

[ 14277]
Correct name of PL_OP_SLAB_ALLOC

[ 14271]
Regen embed enable slab for PERL_IMPLICIT_SYS

[ 14269]
Typo in #else branch of PL_SLAB_ALLOC

[ 14268]
const-ness fix in savepv's passing of NULL

[ 14267]
Hand merge of non slab allocator stuff

[ 14259]
Use PerlMemShared for CopSTASHPV and CopFILE.  MUCH harder than it sounds!
Need to use CopXXXXX macros everywhere and add CopSTASH_free
Add new scope type and add support for it to scope.c and scope stack
dup-er in sv.c. Add savesharedpv().
Also zealous version of Win32's vmem.h to catch all the abuses.
With this t/op/fork.t passes even with zealous checking and
checker is point a finger at various threads/shared issues.
PL_curcop->cop_io is still an issue.

[ 14257]
Inverted sense of special-ness of specialCopIO - supposed to
be true if value is "special" i.e. NOT an SV.

p4raw-link: @14281 on //depot/perlio: 5a8e194fce7241d2bd0867584a5f8b0c0e672556
p4raw-link: @14277 on //depot/perlio: 6916a0abaebd67f9eaa2ffb20dbbb5aaf1b1719d
p4raw-link: @14271 on //depot/perlio: ba979b3106a5e7f3b2512d1f4e93c681fba7aa9f
p4raw-link: @14269 on //depot/perlio: a594c7b4495766324bc28504b0f4af2b5424ed02
p4raw-link: @14268 on //depot/perlio: 965155cb95a9be50d5ff126b516ea1fda1cb74ee
p4raw-link: @14267 on //depot/perlio: 00ca71c18f4e3a59b9a40525cbef41f099448920
p4raw-link: @14259 on //depot/perlio: 05ec9bb346c404c8906ed1ac374d4bce61c84f5d
p4raw-link: @14257 on //depot/perlio: b47b7e599cdd7224bc23222ddfd89205dbb5c997

p4raw-id: //depot/perl@14284