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

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++;
	}
    }