Integrate perlio:

[ 12462]
PerlIOXxxx_dups for all but Win32

[ 12461]
Implement PerlIOStdio_dup (explains core dumps - dup
was not setting up a FILE * to be fclosed()).

[ 12460]
When USE_ITHREADS avoid SV * in PerlIO_debug, at risk of buffer
overflow.

[ 12456]
Builds under ithreads (but fails all threads tests)

[ 12451]
Skeleton of "PerlIO_dup" coded.
Still-passes all tests non-threaded (well it would wouldn't it!)

[ 12447]
Beginings of PerlIO_dup support (unstable)

[ 11615]
Avoid testing for (non-)existance of "encoding(xxxx)"
layer is called "encoding" the (xxxx) is an argument.

p4raw-link: @12462 on //depot/perlio: 9f16d962dace601f24c23063432e8a8eb01bfa4a
p4raw-link: @12461 on //depot/perlio: b77c74bc90789599ae69b0d39a1984d2768fa05e
p4raw-link: @12460 on //depot/perlio: 70ace5dac0395f9f5ca5478d23db8cd1e0dbd6e7
p4raw-link: @12456 on //depot/perlio: a8fc9800e47fd3c23e88282f4505c051278ccc9b
p4raw-link: @12451 on //depot/perlio: 8cf8f3d16d82d8b3561907820401eea7766f2f96
p4raw-link: @12447 on //depot/perlio: 71200d45e1b06d4f36df595fa80b743f999642c1
p4raw-link: @11615 on //depot/perlio: 97ed432b8a5d63d1b7bdda09343e34225e6da722

p4raw-id: //depot/perl@12463