Integrate perlio:

[ 15698]
Fix segfaults when mainthread exits with other threads running:
- track number of running threads
- if main thread calls perl_destruct() with other threads running
skip most of cleanup (with a warning).

[ 15696]
Add -hiertype option to xsubpp for easier mapping C++ with namespaces.
p4raw-link: @15698 on //depot/perlio: 62375a601d6dbbc42fa6d70d83d0a60b73d1b86d
p4raw-link: @15696 on //depot/perlio: 0ab125c1e00cef4eab6989366621d77be6d38567

p4raw-id: //depot/perl@15699

diff --cc embed.fnc
Simple merge

diff --cc perl.h
Simple merge