C: revert 205fbbca Special-case io_close, move PerlIO_cleanup after sv_clean_objs

the cause for the io_close problem was that PerlIO_cleanup was called before sv_clean_objs.
global destruction -O3 looks better now
Fixes #302 CORE--op--utf8cache.t, CORE--op--lex_assign.t, CORE--io--openpid.t
t/manifest.t: added (unix only)

compare MANIFEST to `git ls-tree -r --name-only HEAD >MANIFEST.git`
dos2unix t/z_pod.t