Integrate perlio:

[  8085]
Finish 1st pass of "encoding" layer e.g. :
open($fh,"<encoding(iso8859-7)",$greek) || die;

[  8082]
Restore mmap function (broken by tweaks to shared buffer
layer for encode(xxxx)).

[  8076]
Not merge worthy...
Allow arg to layers e.g. open($fh,"<:encode(iso8859-15)",$name)
syntax is modelled on attributes.
Untested fix for io/utf8 on Win32 etc.
Very clumsy start to the encode layer.

p4raw-link: @8085 on //depot/perlio: 72e44f29ea535faa4a4afab64f5101668334125d
p4raw-link: @8082 on //depot/perlio: a5262162c2c854ee96768d32ed06a8df25b95505
p4raw-link: @8076 on //depot/perlio: 33af2bc731cf870df7b094c6b3d116322b4b493f

p4raw-id: //depot/perl@8087

diff --cc perlio.c
Simple merge