The old code said

	if(x) {
		handle a
		return
	}
	aa = *a
	rewrite aa to make x true
	recursivecall(&aa)

The new code says

	params = copy out of a
	if(!x) {
		rewrite params to make x true
	}
	handle params

but it's hard to see that in the Rietveld diffs because
it gets confused by changes in indentation.

Avoiding the recursion makes other changes easier.

R=ken2
CC=golang-dev
https://golang.org/cl/2533041