Fix qsort

The current implementation of qsort here double counts instances of x... we should fix that.

On a different note... I feel like in the future we shouldn't need `assert_smaller` here at all, since `xs` is guaranteed to be smaller than `x :: xs` (and filter can never make a list larger).
Merge pull request #36 from jthemphill/patch-1

Fix qsort implementation in totality section