Avoid copying string backing when returning from parse function

Avoid copying string backing when returning from parse function

This is a somewhat nasty hack to avoid making a copy of the output
when it comes time to return from the function. For the time being
it will only work with Ruby 1.8.x, or at least, 1.9.x hasn't been
tested yet.

Signed-off-by: Wincent Colaiuta <win@wincent.com>