Fix makeIntIndex, benchmark get loc
- [x] tests passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

``makeIntIndex`` currently produces a monotonic index, and hence tests common to different classes actually test very different things (i.e. the sorted vs. unsorted code paths). I had to fix this (and to fix the tests which erroneously relied on the specific content of ``makeIntIndex(k)``) in order to add meaningful performance tests for ``get_loc``.
