Use PerlMemShared for CopSTASHPV and CopFILE. MUCH harder than it sounds!

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.

p4raw-id: //depot/perlio@14259