Integrate perlio:

[ 15904]
Disable test code (assertions) in CRLF layer.

[ 15903]
Avoid expensive paranoid check that decoder does return legal UTF-8
p4raw-link: @15904 on //depot/perlio: 3b4bd3fd9ce156dd5810f53e7d2c862917be2cb9
p4raw-link: @15903 on //depot/perlio: 3c49ab0895e2c3f761f88c5acb6e1dc985476785

p4raw-id: //depot/perl@15909