Integrate from perlio:

[ 18539]
Try the invalidate_fileno() idea for non-leaky stdio sockets.

[ 18540]
stdio does NOT set errno==EBADF on invalidated fileno

[ 18547]
Tweak APItest for new semantics of printf.
Now printf() is always real printf() and not #define'd to
PerlIO_stdoutf() so PerlIO_flush() when STDOUT is redirected
back to original file does not affect stdout unless we are
using :stdio as implementation. So things printf()ed XS side
are not written to file (and turn up at end of test).
So add an XS function which does fflush(stdout), modify .pm
file to export it and .t file to call it.

[ 18548]
Add defined(__osf__) case to invalidate_fileno (for Tru64).

[ 18549]
Report layer name (without arg) on fail, and attempt to
autoload layer name. (Fix for [perl #20460]).

[ 18550]
#if defined(__irix__) (for stdio invalidate) from Jarkko.
p4raw-link: @18550 on //depot/perlio: 9837d3731bea1e0d3aaed58a46127574f76ffe53
p4raw-link: @18549 on //depot/perlio: c7732655732824f25d1659f5ebb5d4c3538d32e8
p4raw-link: @18548 on //depot/perlio: 9110aad070a9791bfefe4a0d1718537633723305
p4raw-link: @18547 on //depot/perlio: 9d9116831508c6c9cd81c32834701af14b7647a4
p4raw-link: @18540 on //depot/perlio: e85294730ea95da49196ebe8f63ce0db11ebd231
p4raw-link: @18539 on //depot/perlio: 0d7a53989a672378609205d638df0119542bcf7e

p4raw-id: //depot/perl@18555

diff --cc perlio.c
index de6950b,d9cfc39..79f75d3
--- 1/perlio.c
--- 2/perlio.c
+++ b/perlio.c
@@@ -2730,11 -2836,9 +2836,8 @@@ PerlIOStdio_close(pTHX_ PerlIO *f
        }
        return result;
      } 
--
  }
  
- 
- 
  SSize_t
  PerlIOStdio_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
  {