Integrate perlio:

[  8511]
Make "real" layers of ":utf8" and ":raw".
So now PERLIO=utf8 perl ...
does what Andreas wanted.
Fix arg passing in open.pm (still have a Carp issue).

[  8508]
Switch "compiled in" encodings to .ucm format.
(Leave others as .enc till we can run-time load .ucm,
or find some other way to load them.)

p4raw-link: @8511 on //depot/perlio: dfebf9581083f76d0f88d6a3edc9e5b72e852d91
p4raw-link: @8508 on //depot/perlio: e03ac09223e234f57407d65d0cb9cc67f3394e0a

p4raw-id: //depot/perl@8512