Integrate:

Integrate:
[ 19203]
Introduce PerlIO::get_layers() to allow people to peek
at the PerlIO layer stack.
p4raw-link: @19203 on //depot/perl: 39f7a87036eb8d13c207511143dc7f2e620b3891

p4raw-id: //depot/maint-5.8/perl@19259
p4raw-integrated: from //depot/perl@19258 'copy in' perlio.c (@19120..)
	t/io/open.t (@19173..)
p4raw-branched: from //depot/perl@19203 'branch in' t/io/layers.t
p4raw-integrated: from //depot/perl@19203 'copy in' lib/PerlIO.pm
	(@18135..) perlio.h (@18801..) 'merge in' universal.c
	(@18801..) MANIFEST (@19196..)