Filehandle method calls load IO::File on demand

When a method call on a filehandle would die because the method can not
be resolved and L<IO::File> has not been loaded, Perl now loads IO::File
via C<require> and attempts method resolution again:

  open my $fh, ">", $file;
  $fh->binmode(":raw");     # loads IO::File and succeeds

This also works for globs like STDOUT, STDERR and STDIN:

  STDOUT->autoflush(1);

Because this on-demand load only happens if method resolution fails, the
legacy approach of manually loading an IO::File parent class for partial
method support still works as expected:

  use IO::Handle;
  open my $fh, ">", $file;
  $fh->autoflush(1);        # IO::File not loaded

1 files changed, 1 insertions, 0 deletions

diff --git a/MANIFEST b/MANIFEST
index 5ddf5ccc2d..d9281f462a 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -4485,6 +4485,7 @@ t/io/errno.t			See if $! is correctly set
 t/io/fflush.t			See if auto-flush on fork/exec/system/qx works
 t/io/fs.t			See if directory manipulations work
 t/io/inplace.t			See if inplace editing works
+t/io/iofile.t			See if we can load IO::File on demand
 t/io/iprefix.t			See if inplace editing works with prefixes
 t/io/layers.t			See if PerlIO layers work
 t/io/nargv.t			See if nested ARGV stuff works