Fix bug in iPickBounded; don't introduce a disjunction when translating <=

This patch fixes the bug I reported on the issue tracker. The calculations in `iPickBounded` were a bit off. I haven't included the QuickCheck property I used to find the bug, since I didn't want to introduce an extra dependency on QuickCheck, but it's there in the issue tracker if you want to add it.

I also included a patch which reduces <= to < instead of introducing a disjunction.