Grappalang features

This is a few PRs rolled into one.

- 2 key group by
- join swapping and a way to enable it
- make COUNT(a) do local combiner
- include a way to run grappa tests (was not possible to turn off SkipTest)
- tests: matrix multiply, sp2bench Q2, join swapping
can you move the `Chdir` up so that the dot files get created in the test dir rather than root?