Integrate perlio:

[ 16018]
Fill in the PERLIO sections.

[ 16017]
Add :bytes to POD part.
Remove 'alias' to Encode now it exists as a module.

[ 16014]
Tweak to Encode.xs to avoid buffer overrun.

[ 16007]
Silence warning generating warning message for U+FFFF does not map etc.

[ 15912]
XS versions of encode/decode for Encode::Unicode
p4raw-link: @16018 on //depot/perlio: 44a4342c9f1bf4dd16241a6721340a5828ede477
p4raw-link: @16017 on //depot/perlio: c1a61b17baa5d77173aa89ea26a8e563597258e5
p4raw-link: @16014 on //depot/perlio: 0172fc7f023949162f3e79310fb0db0dd22a98f1
p4raw-link: @16007 on //depot/perlio: c6a7db43c3667911196e8ad7c6a3ad53333f3cf3
p4raw-link: @15912 on //depot/perlio: d5c9ee33b57c6c516247cc68878006fd91166a49

p4raw-id: //depot/perl@16019