fully short-circuit &&, ||, //

Currently in an expression like (A || B || C || D), if A is true, then
B, C and D aren't evaluated, but the 2nd, 3rd and 4th OR ops are *still*
executed. Use the peephole optimiser to bypass them.

i.e. change the op tree from

    - A - OR - OR - OR - X---
            \ /  \ /  \ /
             B    C    D
to
    - A - OR --------------------X---
            \                   /
             B - OR -----------/
	           \          /
		    C - OR --/
		          \ /
			   D

With this, the following code's execution time reduces from 1.6s to 0.9s
approx on my system:

    my $a = 1; my $b = 0; my $x = 0;
    for (1..10_000_000) {
	if ($a || $b || $b || $b || $b || $b) {
	    $x++;
	}
    }

1 files changed, 3 insertions, 0 deletions

diff --git a/op.c b/op.c
index 1ad20745b2..7b129ac334 100644
--- a/op.c
+++ b/op.c
@@ -9623,6 +9623,9 @@ Perl_rpeep(pTHX_ register OP *o)
             sop = fop->op_sibling;
 	    while (cLOGOP->op_other->op_type == OP_NULL)
 		cLOGOP->op_other = cLOGOP->op_other->op_next;
+	    while (o->op_next && (   o->op_type == o->op_next->op_type
+				  || o->op_next->op_type == OP_NULL))
+		o->op_next = o->op_next->op_next;
 	    DEFER(cLOGOP->op_other);
           
           stitch_keys: