Integrate perlio:

[ 14536]
Stable intermediate point in Encode cleanup.
:encode(euc-jp) works on Dan's table.euc
Much buffer copying and other silliness remains.

p4raw-link: @14536 on //depot/perlio: 0b3236bb1fb664bc9c9ccd069cac189e80c3ef35

p4raw-id: //depot/perl@14538