Change newSVpvn("…", …) to newSVpvs("…")

The dual-life dists affected use Devel::PPPort, so can safely use
newSVpvs() even though it wasn't added until Perl v5.8.9.
test for the Data::Dumper bug fixed by "Change newSVpvn("…", …) to newSVpvs("…")"
Change sv_catpvn(…, "…", …) to sv_catpvs(…, "…")

The dual-life dist affected uses Devel::PPPort, so can safely use
sv_catpvs() even though it wasn't added until Perl v5.8.9.
bump $VERSION for PerlIO-encoding, PerlIO-mmap, PerlIO-scalar, OS2-Process