Integrate perlio:

Integrate perlio:

[  8927]
Change method names in Encode implementation classes to something
less confusing (preparing to "go public").

[  8926]
GCC __atribute__ / printf fix

[  8925]
Checked in the wrong one ...

[  8923]
Encode API documentation nd tidy up.
Minor additions to test.
Tweaks sv_utf8_upgrade() to force SvPV, and always SvUTF8_on and return length.
Adds STRLEN to standard typemap.

p4raw-link: @8927 on //depot/perlio: 50d2698546d7dba5ed48b29bf1c13887b041a4ba
p4raw-link: @8926 on //depot/perlio: c745e42cb33cb9fcfc4d47fe732cfa4725aa5d07
p4raw-link: @8925 on //depot/perlio: 2a936312a7ab627c98624c1ea83115246309b3d7
p4raw-link: @8923 on //depot/perlio: 4411f3b60960504e67715e05eb0ed3192bfff8fc

p4raw-id: //depot/perl@8934