Integrate perlio:

[ 17587]
Fix :scalar layer to allow it to exist under other layers.
Actual fix is just the if (!f) test before calling
PerlIO_allocate(). Rest of change is conforming to
standard indent.
p4raw-link: @17587 on //depot/perlio: 14d89041d8ff788f94621c8fcb0918e3be8f01f0

p4raw-id: //depot/perl@17594