Integrate perlio:

Integrate perlio:

[ 13959]
Win32 stuff:
A. Use Perl_my_socketpair()
B. Use PerlSock_xxxx() rather than raw xxxx() so we get to load winsock.
C. (In passing) work round fact that $$ is now SvREADONLY so we need to
take special measures to set it during pseudo-fork.

p4raw-link: @13959 on //depot/perlio: e10bb1e95b6ccccae69758ba14c120c19396b201

p4raw-id: //depot/perl@13961