Many plugins only define a puts method on the output object. This change
removse the ability to customize the formatter used when outputting
variables in `ls`. We should reconsider the best way to do this.
This is working around (another) brokenness in jruby 1.6.8s splat
handling in ruby 1.9 mode; but I figure that now jruby 1.7 is out,
we can not bother fixing it.