Ensure that t/io/{print,read,say}.t load Errno at BEGIN time.

Ensure that t/io/{print,read,say}.t load Errno at BEGIN time.

If Errno is loaded after the compiler has parsed the C<exists &Errno::EBADF>
later in the script, then the intent of that test is subverted - &Errno::EBADF
does not exist, at least as far as the typeglob bound to that op is concerned,
and the test for $! is skipped. I suspect that these have been skipping since
the implementation of Errno was changed in 42607a60df6df19b in May 2010 to
reduce its memory footprint by 55%.