no warnings 'safesyscalls', fatal \0 checks

Disallow binary pathnames and arguments to other syscalls, strings
with embedded \0, which are ignored in the syscall but kept in
perl. These invalid string args cause always unnoticed problems,
as they are ignored by the syscalls but kept around in perl.
ExtUtils-Manifest-1.62_01: fix safesyscalls, no double \0 for open()

cp_if_diff used an old-style open(F,"< $from\0") to force an ending \0,
which is not needed with 3arg open, and leads to safesyscalls errors.