Integrate perlio:

[  7796]
Win32 builds and runs (mostly) with USE_PERLIO.
PERLIO=perlio passes all tests.
PERLIO=stdio (sadly the default) hangs in t.pragma/warnings.t #319

[  7790]
If we use (aTHX_ ...) then put Perl_ on the front. (Or drop the aTHX_).

[  7788]
Make extra buffer layer work (dummy crlf layer)

p4raw-link: @7796 on //depot/perlio: 83b075c35b61a28ca7e2629bb5d6e26f9e0354fe
p4raw-link: @7790 on //depot/perlio: efeab7a8047d7136a0235c1cc7329f57d6a8bfdd
p4raw-link: @7788 on //depot/perlio: 88b61e10dfef3b0642d1458a9fff93e5000f86b0

p4raw-id: //depot/perl@7797

diff --cc doio.c
Simple merge

diff --cc perlio.c
Simple merge

diff --cc perlio.h
Simple merge