Integrate perlio:

[ 13409]
Skip socket-ness tests on handles (e.g. PerlIO::Scalar) which do not
have file descriptors. Noticed a possibly worse problem in the process ...

p4raw-link: @13409 on //depot/perlio: e99cca918766541e5f35aa228351805d2bf99e8f

p4raw-id: //depot/perl@13418