&CORE::binmode()

This commit allows &CORE::binmode to be called through references and
via ampersand syntax.

Usually, an op that has optional arguments has the number of arguments
indicated with flags on the op itself:

1 files changed, 10 insertions, 1 deletions

diff --git a/op.c b/op.c
index 606e086825..02811c622e 100644
--- a/op.c
+++ b/op.c
@@ -7685,7 +7685,16 @@ Perl_ck_fun(pTHX_ OP *o)
 	    tokid = &kid->op_sibling;
 	    kid = kid->op_sibling;
 	}
-	if (kid && kid->op_type == OP_COREARGS) return o;
+	if (kid && kid->op_type == OP_COREARGS) {
+	    bool optional = FALSE;
+	    while (oa) {
+		numargs++;
+		if (oa & OA_OPTIONAL) optional = TRUE;
+		oa = oa >> 4;
+	    }
+	    if (optional) o->op_private |= numargs;
+	    return o;
+	}
 
 	while (oa) {
 	    if (oa & OA_OPTIONAL || (oa & 7) == OA_LIST) {