Integrate perlio:

[  9106]
regcomp.c is working in native space, not Unicode space (if different)
as it is doing compare against 'W' in \W etc.

[  9105]
Audit #ifdef EBCDIC and #ifndef ASCIIish, replace latter with former.
Use ASCII_TO_NATIVE and NATIVE_TO_ASCII to avoid some #ifs.

[  9104]
Put utf8_downgrade in CRIPPLED_CC versions of SvPVbyte* before I forget.

[  9102]
USE_SFIO issues as observed by Chris Nandor <pudge@pobox.com>
- exclude layer syms in makedef.pl for sfio
- also inhibit Encode from trying to build ":encode()" layer.

p4raw-link: @9106 on //depot/perlio: 5e12f4fbf2391bc262df1da61c1745c66dc76d71
p4raw-link: @9105 on //depot/perlio: c7f1f0165ac822994a67426c2d8003c3974e49ef
p4raw-link: @9104 on //depot/perlio: ffebcc3e6acf9636047196271385e91b0490ae34
p4raw-link: @9102 on //depot/perlio: 9df9a5cd21960315c39a8675579b46e68b5402c2

p4raw-id: //depot/perl@9107