Integrate perlio:

[  9455]
DLL name has changed so installperl needs to know
(Why isn't it working it out or passed it?)

[  9454]
Change Encode's check arguments to 'bool' so SvTRUE gets used
and we don't get undef warnings.

p4raw-link: @9455 on //depot/perlio: b962b4faa5c1d38e1b3dee493c58991ae48cefe9
p4raw-link: @9454 on //depot/perlio: 691638dd8feb154ca6f21357dad133b313dac373

p4raw-id: //depot/perl@9456