Integrate perlio:

[  8467]
"Safe" signals - trial implementation.
gv.c tweaked to zero PL_sig_pend array
perlio.c tweaked to PERL_ASYNC_CHECK() on EINTR
util.c tweaked to not set SA_RESTART to give perlio.c a chance.
Odd thing is that it "works" with PERLIO=stdio as well (linux).

p4raw-link: @8467 on //depot/perlio: 0a8e0eff0300ee74cef43b18ff11d05a6376450e

p4raw-id: //depot/perl@8468