Integrate perlio:

[  9199]
Prefer !UTF8_IS_INVARIANT() over UTF8_IS_CONTINUED() when that
is the sense of the test being done. Avoid some magical 127 and 128 values
by using macros.

[  9198]
UTF-X encoding invariance for Encode:
- move Encode::utf8_encode to utf8::encode (likewise decode,upgrade,downgrade,valid)
- move the XS code for those to universal.c (so in miniperl)
- add utf8::unicode_to_native and its inverse to allow EBCDIC to work in true unicode.
- change ext/Encode/compile to use above.
- Fix t/lib/encode.t for above
- Teach t/lib/b.t to expect -uutf8
- In utf8.c look for SWASHNEW rather than just utf8:: package to see if
utf8.pm is needed.

[  9196]
Fix pragma/utf8.t # 15
- if toke.c is processing a SvUTF8 string then single quoted '...' etc.
are SvUTF8 as well.

p4raw-link: @9199 on //depot/perlio: 63cd067459124b5dc1d2ae98453df4ffdff11607
p4raw-link: @9198 on //depot/perlio: 1b026014ba0f5424fabe070eda050db5e7df518a
p4raw-link: @9196 on //depot/perlio: be4731d2ab91c4f6213bf88a0084f6128a0db383

p4raw-id: //depot/perl@9200