Integrate from perlio:

[ 19474]
Tweaks to Jarkko's NULL deref checks in perlio.c

[ 19475]
Fix for bugs 21717 and 22140.
Win32's lseek claims to have succeeded in pipes etc. Which confuses :perlio
and derived layers. So have :unix's "pushed" method stat() the fd and
cache non S_ISREG nature. Have Unix_seek fail if fd is NOT S_ISREG to match
UNIX behaviour.

[ 19479]
Better but still unproven fix for lseek() on pipes.

[ 19483]
Unused variable

[ 19485]
Tests to prove Ticket 9468 is fixed.

[ 19486]
add test for change#19475,19479 (bugs#21717,22140)
p4raw-link: @19486 on //depot/perlio: a6dd04483cb30505dd31342b8e0d790b3545179d
p4raw-link: @19485 on //depot/perlio: 317758861cdb698a2ee0bd53db0677ccd65a9eb2
p4raw-link: @19483 on //depot/perlio: acbd16bfa8cc0ce2f8cf72ca650c798b69c28dcc
p4raw-link: @19479 on //depot/perlio: aa063c351bd93493dd45b11fa59e0e5a90b4b421
p4raw-link: @19475 on //depot/perlio: 6caa5a9cfe39f91bc44bba937a0b491f754fe9cd
p4raw-link: @19474 on //depot/perlio: 37725cdcc38b517ef70773e843427b086c3d89e1

p4raw-id: //depot/perl@19487