Test of references in the presence of shadowing.

-- go.mod --
module example.com
go 1.12

-- a/a.go --
package a

func _() {
	x := 123 //@loc(x1, "x"), refs("x", x1, x1ref)
	_ = x //@loc(x1ref, "x")
	{
		x := "hi" //@loc(x2, "x"), refs("x", x2, x2ref)
		_ = x //@loc(x2ref, "x")
	}
}