[perl #126292] [BUG] feeds don't correctly append to an argument list anymore

[Larry Wall via RT]

Whoops, posted the wrong examples.  These actually show the difficulty:

> p6 'say() <== map { $_ * 2 } <== 1...10'
(2 4 6 8 10 12 14 16 18 20)
> p6 'say() <== map { $_ * 2 },0 <== 1...10'
(0 20)

So this really looks like an insidious case of accidental one-arg semantics.